15000 bài tập tách từ đề thi thử môn Tiếng Anh có đáp án (Phần 20)

What geologists call the Basin and Range Province in the United States roughly coincides in its northern portions with the geographic province known as the Great Basin. The Great Basin is hemmed in west by the Sierra Nevada and on the east Line by the Rocky Mountains; it has no outlet to the sea. The prevailing winds in the Great Basin are from the west. Warm, moist air from the Pacific Ocean is forced upward as it crosses the Sierra Nevada. At the higher altitudes it cools and the moisture it carries is precipitated as rain or snow on the western slopes of the mountains. That which reaches the Basin is air wrung dry of moisture. What little water falls there as rain or snow, mostly in the winter months, evaporates on the broad, flat desert floors. It is, therefore, an environment in which organisms battle for survival. Along the rare watercourses, cottonwoods and willows eke out a sparse existence. In the upland ranges, pinion pines and junipers struggle to hold their own.

But the Great Basin has not always been so arid. Many of its dry, closed depressions were once filled with water. Owens Valley, Panamint Valley, and Death Valley were once a string of interconnected lakes .The two largest of the ancient lakes of the Great Basin were Lake Lahontan and Lake Bonneville. The Great Salt Lake is all that remains of the latter, and Pyramid Lake is one of the last briny remnants of the former. There seem to have been several periods within the last tens of thousands of years when water accumulated in these basins. The rise and fall of the lakes were undoubtedly linked to the advances and retreats of the great ice sheets that covered much of the northern part of the North American continent during those times. Climatic changes during the Ice Ages sometimes brought cooler, wetter weather to mid latitude deserts worldwide, including those of the Great Basin. The broken valleys of the Great Basin provided ready receptacles for this moisture.

Coincident with concerns about the accelerating loss of species and habitats has been a growing appreciation of the importance of biological diversity, the number of species in a particular ecosystem, to the health of the Earth and human well-being. Much has been written about the diversity of terrestrial organisms, particularly the exceptionally rich life associated with tropical rain-forest habitats. Relatively little has been said, however, about diversity of life in the sea even though coral reef systems are comparable to rain forests in terms of richness of life.

An alien exploring Earth would probably give priority to the planet's dominant, most-distinctive feature ― the ocean. Humans have a bias toward land that sometimes gets in the way of truly examining global issues. Seen from far away, it is easy to realize that landmasses occupy only one-third of the Earth's surface. Given that two- thirds of the Earth's surface is water and that marine life lives at all levels of the ocean, the total three-dimensional living space of the ocean is perhaps 100 times greater than that of land and contains more than 90 percent of all life on Earth even though the ocean has fewer distinct species.

The fact that half of the known species are thought to inhabit the world's rain forests does not seem uprising, considering the huge numbers of insects that comprise the bulk of the species. One scientist found many different species of ants in just one tree from a rain forest. While every species is different from every other species, their genetic makeup constrains them to be insects and to share similar characteristics with 750,000 species of insects. If basic, broad categories such as phyla and classes are given more emphasis than differentiating between species, then the greatest diversity of life is unquestionably the sea. Nearly every major type of plant and animal has some representation there.

To appreciate fully the diversity and abundance of life in the sea, it helps to think small. Every spoonful of ocean water contains life, on the order of 100 to 100,000 bacterial cells plus assorted microscopic plants and animals, including larvae of organisms ranging from sponges and corals to starfish and clams and much more.

Fifty-five delegates representing all thirteen states except Rhode Island attended the Constitutional Convention in Philadelphia from May to September 1787. The delegates had been instructed by the Continental Congress to revise the old Articles of Confederation, but most believed that a stronger central government was needed. There were differences, however, about what structure the government should take and how much influence large states should have.

Virginia was by far the most populous state, with twice as many as people as New York, four times as many as New Jersey, and ten times as many as Delaware. The leader of the Virginia delegation, James Madison, had already drawn up a plan for government, which became known as the Large State Plan. Its essence was that congressional representation would be based on population. It provided for two or more national executives. The smaller states feared that under this plan, a few large states would lord over the rest. New Jersey countered with the Small State Plan. It provided for equal representation for all states in a national legislature and for a single national executive. Angry debate, heightened by a stifling heat wave, led to deadlock.

A cooling of tempers seemed to come with lower temperatures. The delegates hammered out an agreement known as the Great Compromise- actually a bundle of shrewd compromises. They decided that Congress would consist of two houses. The larger states were granted representation based on population in the lower house, the House of Representatives. The smaller states were given equal representation in the upper house, the Senate, in which each state would have two senators regardless of population. It was also agreed that there would be a single executive, the president. This critical compromise broke the logjam, and from then on, success seemed within reach.

The biologist's role in society as well as his moral and ethical responsibility in the discovery and development of new ideas has led to a reassessment of his social and scientific value systems. A scientist can no longer ignore the consequences of his discoveries; he is as concerned with the possible misuses of his findings as he is with the basic research in which he is involved. This emerging social and political role of the biologist and all other scientists requires a weighing of values that cannot be done with the accuracy or the objectivity of a laboratory balance. As a member of society, it is necessary for a biologist now to redefine his social obligations and his functions, particularly in the realm of making judgments about such ethical problems as man's control of his environment or his manipulation of genes to direct further evolutionary development.

As a result of recent discoveries concerning hereditary mechanisms, genetic engineering, by which human traits are made to order, may soon be a reality. As desirable as it may seem to be, such an accomplishment would entail many value judgments. Who would decide, for example, which traits should be selected for change? In cases of genetic deficiencies and disease, the desirability of the change is obvious, but the possibilities for social misuse are so numerous that they may far outweigh the benefits.

Probably the greatest biological problem of the future, as it is of the present, will be to find ways to curb environmental pollution without interfering with man's constant effort to improve the quality of his life. Many scientists believe that underlying the spectra of pollution is the problem of surplus human population. A rise in population necessitates an increase in the operations of modern industry, the waste products of which increase the pollution of air, water, and soil. The question of how many people the resources of the Earth can support is one of critical importance.

Although the solutions to these and many other problems are yet to be found, they do indicate the need for biologists to work with social scientists and other members of society in order to determine the requirements necessary for maintaining a healthy and productive planet. For although many of man's present and future problems may seem to be essentially social, political, or economic in nature, they have biological ramifications that could affect the very existence of life itself.

George Washington Carver showed that plant life was more than just food for animals and humans. Carver’s first step was to analyze plant parts to find out what they were made of. He then combined these simpler isolated substances with other substances to create new products.

The branch of chemistry that studies and finds ways to use raw materials from farm products to make industrial products is called chemurgy. Carver was one of the first and greatest chemurgists of all time. Today the science of chemurgy is better known as the science of synthetics. Each day people depend on and use synthetic materials made from raw materials. All his life Carver battled against the disposal of waste materials and warned of the growing need to develop substitutes for the natural substances being used up by humans.

Carver never cared about getting credit for the new products he created. He never tried to patent his discoveries or get wealthy from them. He turned down many offers to leave Tuskegee Institute to become a rich scientist in private industry. Thomas Edison, inventor of the electric light, offered him a laboratory in Detroit to carry out food research. When the United States government made him a collaborator in the Mycology and Plant Disease Survey of the Department of Agriculture, he accepted the position with the understanding that he wouldn’t have to leave Tuskegee. As an authority on plant diseases – especially of the fungus variety – Carver sent hundreds of specimens to the United States Department of Agriculture. At the peak of his career, Carver’s fame and influence were known on every continent.

Atomic were once thought to be fundamental pieces of matter, but they are in turn made of smaller subatomic particles. There are three major subatomic particles neutrons, protons, and electronic. Protons and neutrons can be broken into even smaller units, but these smaller units do not occur naturally in nature and are thought to only be produced in manmade particle accelerators and perhaps in extreme stellar events like supernovas. The structure of an atom can best be described as a small solar system, with the neutrons at the center and the electrons circling them in various orbits, just as the planets circle the sun .In reality, the structure of an atom is far more complex, because the laws of physics are fundamentally different at the atomic level than of the level of the observable word. The true nature of atomic structure can only be expressed accurately through complex mathematical formulas .This explanation, however, is of little use to most average people.

Protons and neutrons have nearly equal mass and size, but protons carry a positive electrical charge, while neutrons carry no charge at all. Protons and neutrons are bound together by the strong nuclear force, one of the four basic forces in the universe. Protons and neutrons give atoms some of their most basic properties. Elements are defined by two numbers; their atomic number , which is equal to the number of protons they have, and their atomic weight , which is equal to total number of their neutrons and protons. In most lighter atoms , the number of neutrons and protons is equal , and the element is stable. In heavier atoms, however, there are more neutrons than protons , and the element is unstable, eventually losing neutrons through radioactive decay until a neutral state is reached.

Electrons are negatively charged particles. They are bound to their atoms through electromagnetic attraction. Opposite electrical charges attract one another, so the positive charge of the proton helps keep the negatively charged electron in orbit around the nucleus of the atom. Electrons are different from neutrons in that they cannot be broken down into smaller particles. They are also far smaller and lighter than neutrons and protons. An electron is about one thousandth of the diameter of a proton and an even smaller fraction of its mass. Electrons circle the protons and neutrons at the center of the atom in orbit. These orbits are often called electron shells. The closer the orbit is to the center of the atom, the lower its energy is. There are seven electron shells, and each higher level can hold more electron than the previous shell. Electrons naturally seek to occupy the lowest shell possible .So if there is space in a lower shell, an electron will drop down to occupy that space. At temperatures higher than a few hundred degrees, electrons will gain energy and move to a higher shell, but only momentarily. When the electrons drop back down to their natural shell, they emit light .This is why fires and other very hot objects seem to glow.

Electrons are also primarily responsible for many of the chemical properties of atoms. Since electrons seek to occupy the lowest electron shell possible, they will move from one atom to another if there is a space available in a lower electron shell. For example, if there is an atom with an open space in its third shell, and it comes into contact with an atom with electrons in its fourth shell, the first atom will take one of these electrons to complete its third shell. When this happens, the two atoms will be chemically bonded to form a molecule. Furthermore, atoms sometimes lose electrons in collisions with other atoms. When it happens, the radio of protons and electrons in the atom changes, and therefore, the overall electrical charge of the atom changes as well. These atoms are called isotopes, and they have significantly different chemical properties from their parent atoms.

Animals have an intuitive awareness of quantities. They know without analysis the difference between a number of objects and a smaller number. In his book “ The natural History of Selboure ” (1786 ) , the naturalist Gilbert White tells how he surreptitiously removed one egg a day from a plover‟s nest , and how the mother laid another egg each day to make up for the missing one . He noted that other species of birds ignore the absence of a single egg but abandon their nests if more than one egg has been removed. It has also been noted by naturalists that a certain type of wasp always provides five – never four, never six - caterpillars for each of their eggs so that their young have something to eat when the eggs hatch . Research has also shown that both mice and pigeons can be taught to distinguish between odd and even numbers of food pieces.
          These and similar accounts have led some people to infer that creatures other than humans can actually count. They also point to dogs that have been taught to respond to numerical questions with the correct number of barks, or to horses that seem to solve arithmetic problems by stomping their hooves the proper number of times.
          Animals respond to quantities only when they are connected to survival as a species – as in the case of the eggs – or survival as individuals - as in the case of food. There is no transfer to other situations or from concrete reality to the abstract notion of numbers. Animals can “count” only when the objects are present and only when the numbers involved are small – not more than seven or eight. In lab experiments, animals trained to “count” one kind of object were unable to count any other type. The objects, not the numbers, are what interest them. Animals admittedly remarkable achievements simply do not amount to evidence of counting, nor do they reveal more than innate instincts, refined by the genes of successive generations, or the results of clever, careful conditioning by trainers

Life originated in the early seas less than a billion years after the Earth was formed. Yet another three billion years were to pass before the first plants and animals appeared on the continents. Life’s transition from the sea to the land was perhaps as much of an evolutionary challenge as was the genesis of life.
          What forms of life were able to make such a drastic change in lifestyle? The traditional view of the first terrestrial organisms is based on mega fossils-relatively large specimens of essentially whole plants and animals. Vascular plants, related to modern seed plants and ferns, left the first comprehensive mega fossil record. Because of this, it has been commonly assumed that the sequence of terrestrialization reflected the evolution of modern terrestrial ecosystems. In this view, primitive vascular plants first colonized the margins of continental waters, followed by animals that feed on the plants, and lastly by animals that preyed on the plant-eaters. Moreover, the mega fossils suggest that terrestrial life appeared and diversified explosively near the boundary between the Silurian and the Devonian periods, a little more than 400 million years ago.
          Recently, however, paleontologists have been taking a closer look at the sediments below this Silurian-Devonian geological boundary. It turns out that some fossils can be extracted from these sediments by putting the rocks in an acid bath. The technique has uncovered new evidence form sediments that were deposited near the shores of the ancient oceans- plant microfossils and microscopic pieces of small animals. In many instances the specimens are less than one-tenth of a millimeter in diameter. Although they were entombed in the rocks for hundreds of millions of years, many of them fossils consist of the organic remains of the organism.
          These newly discovered fossils have not only revealed the existence of previously unknown organisms, but have also pushed back these dates for the invasion of land by multicellular organisms. Our views about the nature of the early plant and animal communities are now being revised. And with those revisions come new speculations about the first terrestrial life-forms

Franklin D. Roosevelt, the 32nd president of the United States, was from a wealthy, well-known family. As a child, he attended private school, had private tutors, and traveled with his parents to Europe. He attended Harvard University, and afterward studied law. At age 39 Roosevelt suddenly developed polio, a disease that left him without the full use of his legs for the rest of his life. Even through the worst of his illness, however, he continued his life in politics. In 1924 he appeared at the Democratic National Convention to nominate Al Smith for president, and eight years after that he himself was nominated for the same office. Roosevelt was elected to the presidency during the Great Depression of the 1930s, at a time when more than 5,000 banks had failed and thousands of people were out of work. Roosevelt took action. First he declared a bank holiday that closed all the banks so no more could fail; then he reopened the banks little by little with government support. Roosevelt believed in using the full power of government to help what he called the "forgotten people." And it was these workers, the wage earners, who felt the strongest affection toward Roosevelt. There were others, however, who felt that Roosevelt's policies were destroying the American system of government, and they opposed him in the same intense way that others admired him.

In 1940 the Democrats nominated Roosevelt for an unprecedented third term. No president in American history had ever served three terms, but Roosevelt felt an obligation not to quit while the United States' entry into World War II was looming in the future. He accepted the nomination and went on to an easy victory.

After two decades of growing student enrollments and economic prosperity, business schools in the United States have started to face harder times. Only Harvard's MBA School has shown a substantial increase in enrollment in recent years. Both Princeton and Stanford have seen decreases in their enrollments. Since 1990, the number of people receiving Masters in Business Administration (MBA) degrees, has dropped about 3 percent to 75,000, and the trend of lower enrollment rates is expected to continue.

There are two factors causing this decrease in students seeking an MBA degree. The first one is that many graduates of four-year colleges are finding that an MBA degree does not guarantee a plush job on Wall Street, or in other financial districts of major American cities. Many of the entry-level management jobs are going to students graduating with Master of Arts degrees in English and the humanities as well as those holding MBA degrees. Students have asked the question, "Is an MBA degree really what I need to be best prepared for getting a good job?" The second major factor has been the cutting of American payrolls and the lower number of entry-level jobs being offered. Business needs are changing, and MBA schools are struggling to meet the new demands.