15000 bài tập tách từ đề thi thử môn Tiếng Anh có đáp án (Phần 17)

The ruined temples of Angkor are perhaps one of the most impressive Seven Wonders of the World. Located in modern day Cambodia near Lake Tonle Sap, the largest freshwater lake in Asia, Angkor was the seat of power for the Khmer Empire for the ninth to the fifteenth century. The ruins of Angkor are documented as some of the most impressive ones in the world, rivaling the pyramids of Giza in Egypt. Why this mighty civilization died out is a question that archeologists are now only beginning to ponder. The answer, it turns out, may be linked with the availability of fresh water.

One possible explanation for the downfall of the Khmer Empire has to do with the inhabitant’s irrigation system. The temples and palaces of Angkor were constructed around a series of artificial reservoirs and canals which were annually flooded to capacity by the Mekong River. Once filled, they were used to irrigate the surrounding paddies and farmland during the course of the year. Farmers were completely dependent on the water for water crucial rice crop. Without consistent irrigation, the farmers would have been unable to maintain functional crop production.

Scientists speculate that toward the end of the Khmer Empire the hydraulic system of the reservoirs and canals broke down. The construction of hundreds of sandstone temples and palaces required an enormous amount of physical labor. In addition, as the capital of Khmer Empire, Angkor contained upwards of one hundred thousand people who resided in and around Angkor. In order to feed so many people, the local farmers were driven to grow food more quickly and more efficiently. After centuries of continual use, the irrigation system was pushed beyond its capacity. Soil erosion, nutrient depletion, and loss of water led to decrease in the food supply. With the less food available, the people of Angkor slowly began to migrate to other parts of Cambodia, thus leaving the marvelous city of Angkor to be swallowed by the jungle. Therefore, it is speculated that the Khmer Empire may have fallen victim to its own decrepit infrastructure.

The quest for sustainable sources of energy study the energy has led humans to study the energy potential of the sun and the wind, as well as the immense power created by dammed rivers. The oceans, too, represent an impressive source of potential energy. For example, it has been estimated that the oceans could provide nearly 3,000 times the energy generated by hydroelectric dams such as the Hoover Dam. Yet, this source remains quite difficult to exploit.

But this challenge has not prevented scientists from trying. Within the last few decades, several technologies that can transform the ocean’s immense forces into usable electricity have been invented and introduced. Some focus on capturing the power of the changing tides, while others rely on thermal energy created by oceans in certain tropical regions. However, the most common and easiest-to-develop technologies are those designed to harness the power inherent in the ocean’s waves.

There are several methods by which ocean-wave energy can be collected. All of them work because the movement of the water that the waves induce creates storable energy by directly or indirectly driving a power generator. In one such technology, the changing water levels in the ocean that are produced by waves lift a long floating tube comprised of many sections connected by hinges. As the sections move up and down with the water, they pump a special fluid through the tube that can be used to drive a generator. Another technique works on a similar principle, only the floating object rocks back and forth with the motion of the water instead of up and down. A third method of collecting wave energy relies on the rising water from the waves to compress air in a partially submerged chamber. As the waves rush into the chamber, they push the air out through a narrow tunnel. Located inside this tunnel is a turbine connected to a power generator. The movement of the air turns the turbine, which feeds energy into the generator.

The drawback to each of these concepts is that the they make it necessary to have many pieces of machinery linked together. This presents a problem because the larger the device, the more vulnerable it is to damage from hazardous ocean environments, and the more likely it is to interfere with otherwise unspoiled coastal scenery. Also, these methods demand the construction of site-specific machines that take into consideration average local wave heights and sea conditions. Such a requirement can be quite cost-prohibitive, because engineers must create unique power generation mechanism for each site. In other words, the ability to get power from waves differ from region to region.

Japan, Norway, and the UK have attempted to generate energy by capturing the power of ocean waves. In northern Scotland, the first power plan to use wave power, OSPREY ( Ocean Swell Powered Renewable Energy ), began operating in 1995. It followed the principle of the third method described above : waves entering a partially submerged chamber pushed air into turbines to generate electricity. The electricity was then transmitted to power collectors in the shore via underwater cables. Unfortunately, the OSPREY plant was destroyed in a large storm, highlighting an unavoidable difficulty associated with this kind of power generation.

The potential benefits of wave-based energy are hard to ignore. Once the proper machinery is produced and installed, the energy is free. Maintenance cost are small, and the equipment does not pose any threats of environmental pollution. And best of all, the amounts of energy produced are enormous.

However, these theoretical advantages have yet to be fully realized. In many cases, a lack of government funding has inhibited the technologies from advancing. For example, despite the relative abundance of proposed wave-power devices, many have not been adequately tested, and most have been evaluated only in artificial pools where they are not subjected to the harsh marine conditions that exist in actual oceans. Protecting the equipment from the sea’s destructive forces, as well as the fundamental task of determining feasible locations for collecting energy source are substantial and will require more time to overcome.

Telecommuting-substituting the computer for the trip to the job-has been hailed as a solution to all kinds of problems related to office work. For workers, it promises freedom from the office, less time wasted in traffic, and help with child-care conflicts. For management, telecommuting helps keep high performers on board, minimizes tardiness and absenteeism by eliminating commutes, allows periods of solitude for high-concentration tasks, and provides scheduling flexibility. In some areas, such as Southern California and Seattle, Washington, local governments are encouraging companies to start telecommuting programs in order to reduce rush-hour congestion and improve air quality, but these benefits do not come easily. Making a telecommuting program work requires careful planning and an understanding of the differences between telecommuting realities and popular images.

 Many workers are seduced by rosy illusions of life as a telecommuter. A computer programmer from New York City moves to the tranquil Adirondack Mountains and stays in contact with her office via computer. A manager comes into his Office three days a week and works at home the other two. An accountant stays home to care for child; she hooks up her telephone modem connections and does office work between calls to the doctor.

 These are powerful images, but they are a limited reflection of reality. Telecommuting workers soon learn that it is almost impossible to concentrate on work and care for a young child at the same time. Before a certain age, young children cannot recognize, much less respect, the necessary boundaries between work and family. Additional child support is necessary if the parent is to get any work done.

 Management, too, must separate the myth from the reality. Although the media has paid a great deal of attention to telecommuting, in most cases it is the employee’s situation, not the availability of technology, that precipitates a telecommuting arrangement.

 That is partly why, despite the widespread press coverage, the number of companies with work-at-home programs or policy guidelines remains small.

Millions of people tune into the weather forecast each evening on televisions. Most of them imagine that the presenter does little more than arrive at the studio a few minutes before the broadcast, read the weather, and then go home.

In fact, this imagine is far from the truth. The two-minute bulletin which we all rely on when we need to know tomorrow’s weather is the result of a hard day’s work by the presenter, who is actually a highly-qualified meteorologist.

Every morning after arriving at the TV studios, the first task of the days is to collect the latest data from the national Meteorological Office. This office provides up-to-the-minute information about weather conditions throughout the day, both in Britain and around the world. The information is very detailed and includes predictions, satellite and radar pictures, as well as more technical data. After gathering all the relevant material from this office, the forecaster has to translate the scientific terminology and maps into images and word which viewers can easily understand.

The final broadcast is then carefully planned. It is prepared in the same way as other programmes. The presenter decides what to say and in what order to say it. Next, a “story board” is drawn up which lay out the script word for word. What make a weather forecast more complicated than other programmes are the maps and electronic images which are required. The computer has to be programmed so that the pictures appear in the correct order during the bulletin.

The time allocated for each broadcast can also alter. This is because the weather report is screened after the news, which can vary in length. The weather forecaster doesn’t always know how much time is available, which means that he/ she has to be thoroughly prepared so that the material can be adapted to the time available.

Another related complication is that the weather forecast has to be a live broadcast; it cannot be pre- recorded. Live shows are very nerve- racking for the presenter because almost anything can go wrong. Perhaps the most worrying aspect for every weather forecaster is getting the following day’s predictions wrong. Unfortunately for them this is not an unusual occurrence; the weather is not always possible to predict accurately.

The weather is a national obsession in Britain, Perhaps because it is so changeable. It’s the national talking point, and most people watch at least one daily bulletin. It can be mortifying for a weather man or woman who has predicted rain for the morning to wake up to brilliant sunshine. These days, a weather forecaster’s job is even more complicated because they are replied upon to predict other environmental conditions. For example, in the summer the weather forecast has to include the pollen count for hay fever sufferers. Some also include reports on ultraviolet radiation intensity to help people avoid sunburn.

The job of the weather forecaster is certainly far more complicated than just pointing at a map and describing weather conditions. It’s a job for professionals who can cope with stressful and demanding conditions.

Since the world became industrialized, the number of animal species that have either become extinct or near extinction has increased. Bengal tigers, for instance, which once roamed the jungles in vast numbers, now number only about 2,300. By the year 2025, it is estimated that they will become extinct.

 What is alarming about the case of the Bengal tiger is that this extinction will have been caused almost entirely by poachers who, according to some sources, are not always interested in material gain but in personal gratification. This is an example of the callousness that is contributing to the problem of extinction. Animals such as the Bengal tiger, as well as other endangered species, are valuable parts of the world/s ecosystem. International laws protecting animals must be enacted to ensure their survival-and the survival of our planet.

 Countries around the world have begun to deal with the problem in various ways. Some countries, in an effort to circumvent the problem, have allocated large amounts of land to animal reserves. They then charge admission prices to help defray the costs of maintaining the parks, and they often must also depend on world organizations for support. This money enables them to invest in equipment and patrols o protect the animals. Another response to the increase in animal extinction is an international boycott of products made from endangered species. This has had some effect, but by itself will not prevent animals from being hunted and killed.

Though Edmund Halley was most famous because of his achievements as an astronomer, he was a scientist of diverse interests and great skill. In addition to studying the skies, Halley was also deeply interested exploring the unknown depths of the oceans. One of his lesser-known accomplishments that was quite remarkable was his design for a diving bell that facilitated exploration of the watery depths.

The diving bell that Halley designed had a major advantage over the diving bells that were in use prior to his. Earlier diving bells could only make use of the air contained within the bell itself, so divers had to surface when the air inside the bell ran low. Halley's bell was an improvement in that its design allowed for an additional supply of fresh air that enabled a crew of divers to remain underwater for several hours.

The diving contraption that Halley designed was in the shape of a bell that measured three feet across the top and five feet across the bottom and could hold several divers comfortably; it was open at the bottom so that divers could swim in and out at will. The bell was built of wood, which was first heavily tarred to make it water repellent and was then covered with a half-ton sheet of lead to make the bell heavy enough to sink in water. The bell shape held air inside for the divers to breathe as the bell sank to the bottom.

The air inside the bell was not the only source of air for the divers to breathe, and it was this improvement that made Halley's bell superior to its predecessors. In addition to the air already in the bell, air was also supplied to the divers from a lead barrel that was lowered to the ocean floor close to the bell itself. Air flowed through a leather pipe from the lead barrel on the ocean floor to the bell. The diver could breath the air from a position inside the bell, or he could move around outside the bell wearing a diving suit that consisted of a lead bell-shaped helmet with a glass viewing window and a leather body suit, with a leather pipe carrying fresh air from the diving bell to the helmet.

Every year about two million people visit Mount Rushmore, were the faces of four U.S presidents were carved in granite by sculptor Gutzon Borglum and his son, the late Lincoln Borglum. The creation of the Mount Rushmore monument Line took 14 years – from 1927 to 1941 – and nearly a million dollars. There were times when money was difficult to come by and many people were jobless. To move more than 400,000 tons of rock, Borglum hired laid-off workers from the closed-down mines in the Black Hills area. He taught these men to dynamite, drill, carve, and finish the granite as they were hanging in midair in his specially devised chairs, which had many safety features. Borglum was proud of the fact that no workers were killed or severely injured during the years of blasting and carving.

 During the carving, many changes in original design had to be made to keep the carved heads free of large fissures that were uncovered. However, not all the cracks could be avoided, so Borglum concocted a mixture of granite dust, white lead, and linseed oil to fill them.

 Every winter, water from melting snows gets into the fissures and expands as it freezes, making the fissures bigger. Consequently, every autumn maintenance work is done to refill the cracks. The repairers swing out in space over a 500-foot drop and fix the monument with the same mixture that Borglum used to preserve this national monument for future generations.

In the late 1960’s, many people in North America turned their attention to environmental problems and new steel-and-glass skyscrapers were widely criticized. Ecologists pointed out that a cluster of tall buildings in a city often overburdens public transportation and parking lot capacities.

Skyscrapers are also lavish consumers, and waster, of electric power. In one recent year, the addition of 17 million square feet of skyscraper office space in New York City raised the peak daily demand for electricity by 120,-000 kilowatts-enough to supply the entire city of Albany, New York, for a day.

Glass-walled skyscrapers can be especially wasteful. The heat loss (or gain) through a wall of half-inch plate glass is more than ten times that through a typical masonry wall filled with insulation board. To lessen the strain on heating and air-conditioning equipment, builders of skyscrapers have begun to use double glazed panels of glass, and reflective glasses coated with silver or gold mirror films that reduce glare as well as heat gain. However, mirror-walled skyscrapers raise the temperature of the surrounding air and affect neighboring buildings.

Skyscrapers put a severe strain on a city’s sanitation facilities, too. If fully occupied, the two World Trade Center towers in New York City would alone generate 2.25 million gallons of raw sewage each year-as much as a city the size of Stamford, Connecticut, which has a population of more than 109,000.

Skyscrapers also interfere with television reception, block bird flyways, and obstruct air traffic. In Boston, in the late 1960’s some people even feared that shadows from skyscrapers would kill the grass on Boston Common.

Still, people continue to build skyscrapers for all the reasons that they have always built them – personal ambition, civic pride, and the desire of owners to have the largest possible amount of rentable space.

Edward Patrick Francis “Eddie” Eagan (April 26, 1897-June 14, 1967), was an amateur boxing star of the early 1920s. He was born into a poor family in Denver, Colorado. His father died in a railroad accident when Eagan was only a year old. He and his four brothers were raised by his mother, who earned a small income from teaching foreign languages.

Inspired by Frank Merriwell, the hero of a series of popular novels for boys, Eagan pursued an education for himself as well as an interest in boxing. He attended the University of Denver for a year before serving in the U.S. Army as an artillery lieutenant during World War I. After the war, he entered Yale University and, while studying there, won the U.S. national amateur heavyweight boxing title. He graduated from Yale in 1921, attended Harvard Law School, and received a Rhodes scholarship to the University of Oxford where he received his Master’s Degree in 1928.

While studying at Oxford, Eagan became the first American to win the British amateur boxing championship. Eagan won his first Olympic gold medal as a light heavyweight boxer at the 1920 Olympic Games in Antwerp, Belgium. Eagan also fought at the 1924 Olympics in Paris as a heavyweight but failed to get a medal. Though he had taken up the sport just three weeks before the competition, he managed to win a second gold medal as a member of the four-man bobsled team at the 1932 Olympics in Lake Placid, New York. Thus he became the only athlete to win gold medals at both the Summer and Winter Olympics.

Eagan was a member of the first group of athletes inducted into the U.S. Olympic Hall of Fame in 1983. Eagan became a respected attorney, serving as an assistant district attorney for southern New York and as chairman of the New York State Athletic Commission (1945-51). He married soap heiress. Margaret Colgate and attained the rank of lieutenant colonel during World War II. He died at the age of 70, in Rye, New York.

What makes it rain? Rain falls from clouds for the same reason anything falls to Earth. The Earth’s gravity pulls it. But every cloud is made of water droplets or ice crystals. Why doesn’t rain or snow fall constantly from all clouds? The droplets or ice crystals in clouds are exceedingly small. The effect of gravity on them is minute. Air currents move and lift droplets so that the net downward displacement is zero, even though the droplets are in constant motion.

Droplets and ice crystals behave somewhat like dust in the air made visible in a shaft of sunlight. To the casual observer, dust seems to act in a totally random fashion moving about chaotically without fixed direction. But in fact dust particles are much larger than water droplets and they finally fall. The cloud droplet of average size is only 1/2500 inch in diameter. It is so small that it would take sixteen hours to fall half a mile in perfectly still air, and it does not fall out of moving air at all. Only when the droplet grows to a diameter of 1/125 inch or larger can it fall from the cloud. The average raindrop contains a million times as much water as a tiny cloud droplet. The growth of a cloud droplet to a size large enough to fall out is the cause of rain and other forms of precipitation. This important growth process is called “coalescence”.