15000 bài tập tách từ đề thi thử môn Tiếng Anh có đáp án (Phần 64)

Anthropologists have pieced together the little they know about the history of left - handedness and right - handedness from indirect evidence. Though early men and women did not leave written records, they did leave tools, bones, and pictures. Stone Age hand axes and hatchets were made from stones that were carefully chipped away to form sharp cutting edges. In some, the pattern of chipping shows that these tools and weapons were made by right handed people, designed to fit comfortably into a right hand. Other Stone Age implements were made by or for left-handers Prehistoric pictures, painted on the walls of caves, provide further clues to the handedness of ancient people. A right - hander finds it easier to draw faces of people and animals facing toward the left, whereas a left - hander finds it easier to draw faces facing toward the right. Both kinds of faces have been found in ancient painting. On the whole, the evidence seems to indicate that prehistoric people were either ambidextrous or about equally likely to be left - or right - handed.

      But, in the Bronze Age, the picture changed. The tools and weapons found from that period are mostly made for right - handed use. The predominance of right - handedness among humans today had apparently already been established.

 Insects’ lives are very short and they have many enemies, but they must survive long enough to breed and perpetuate their kind. The less insect-like they look, the better their chance of survival. To look "inedible" by resembling or imitating plants is a deception widely practiced by insects. Mammals rarely use this type of camouflage, but many fish and invertebrates do.

     The stick caterpillar is well named. It is hardly distinguishable from a brown or green twig. This caterpillar is quite common and can be found almost anywhere in North America. It is also called "measuring worm" or "inchworm." It walks by arching its body, then stretching out and grasping the branch with its front feet then looping its body again to bring the hind feet forward. When danger threatens, the stick caterpillar stretches its body away from the branch at an angle and remains rigid and still, like a twig, until the danger has passed.

Walking sticks, or stick insects, do not have to assume a rigid, twig-like pose to find protection; they look like inedible twigs in any position. There are many kinds of walking sticks, ranging in size from the few inches of the North American variety to some tropical species that may be over a foot long. When at rest their front legs are stretched out, heightening their camouflage. Some of the tropical species are adorned with spines or ridges, imitating the thorny bushes or trees in which they live.

     Leaves also seem to be a favorite object for insects to imitate. Many butterflies can suddenly disappear from view by folding their wings and sitting quietly among the foliage that they resemble.

Homing pigeons are placed in a training program from about the time they are twenty-eight days of age. They are taught to enter the loft through a trap and to exercise above and around the loft, and gradually they are taken away for short distances in wicker baskets and released. They are then expected to find their way home in the shortest possible time.

In their training flights or in actual races, the birds are taken to prearranged distant points and released to find their way back to their own lofts. Once the birds are liberated, their owners, who are standing by at the home lofts, anxiously watch the sky for the return of their entries. Since time is of the essence, the speed with which the birds can be induced to enter the loft trap may make the difference between gaining a win or a second place.

The head of a homing pigeon is comparatively small, but its brain is one quarter larger than that of the ordinary pigeon. The homing pigeon is very intelligent and will persevere to the point of stubbornness some have been known to fly a hundred miles off course to avoid a storm.

Some homing pigeon experts claim that this bird is gifted with a form of built-in radar that helps it find its own loft after hours of flight, for hidden under the head feathers are two very sensitive ears, while the sharp, prominent eyes can see great distances in daytime.

Why do homing pigeons fly home? They are not unique in this inherent skill: it is found in most migratory birds, in bees, ants, toads, and even turtles, which have been known to travel hundreds of miles to return to their homes. But in the animal world, the homing pigeon alone can be trusted with its freedom and trained to carry out the missions that people demand.

If the salinity of ocean waters is analyzed, it is found to vary only slightly from place to place. Nevertheless, some of these small changes are important. There are three basic processes that cause a change in oceanic salinity. One of these is the subtraction of water from the ocean by means of evaporation-conversion of liquid water to water vapor. In this manner, the salinity is increased, since the salts stay behind. If this is carried to the extreme, of course, white crystals of salt would be left behind: this, by the way, is how much of the table salt we use is actually obtained.

The opposite of evaporation is precipitation. such as rain, by which water is added to the ocean. Here the ocean is being diluted so that the salinity is decreased. This may occur in areas of high rainfall or in coastal regions where rivers flow into the ocean. Thus salinity may be increased by the subtraction of water by evaporation, or decreased by the addition of fresh water by precipitation or runoff.

Normally in tropical regions where the Sun is very strong, the ocean salinity is somewhat higher than it is in other parts of the world where there is not as much evaporation. Similarly, in coastal regions where rivers dilute the sea salinity is somewhat lower than in other oceanic areas.

A third process by which salinity may be altered is associated with the formation and melting of sea ice. When seawater is frozen, the dissolved materials are left behind. In this manner, seawater directly beneath freshly formed sea ice has a higher salinity than it did before the ice appeared. Of course, when this ice melts, it will tend to decrease the salinity of the surrounding water.

In the Weddell Sea, off Antarctica, the densest water in the oceans is formed as a result of this freezing process, which increases the salinity of cold water. This heavy water sinks and is found in the deeper portions of the oceans of the world.

Stars have been significant features in the design of many United States coins and their number has varied from one to foty-eight stars. Most of the coins issued from about 1799 to the early years of the twentieth century bore thirteen stars representing the thirteen original colonies.

  Curiously enough, the first American silver coins, issued in, 1794, had fifteen stars because by that time Vermont and Kentucky had joined the Union. At that time it was apparently the intention of mint officials to add a star for each new state. Following the admission of Tennessee in 1796, for example, some varieties of half dimes, dimes, and half-dollars were produced with sixteen stars.

  As more states were admitted to the Union, however, it quickly became apparent that this scheme would not prove practical and the coins from 1798 on were issued with only thirteen stars-one for each of the original colonies. Due to an error at the mint, one variety of the 1828 half cent was issued with only twelve stars. There is also a variety of the large cent with only 12 stars, but this is the result of a die break and is not a true error.

Icebergs are among nature’s most spectacular creations, and yet most people have never seen one. A vague air of mystery envelops them. They come into being somewhere-in faraway, frigid waters, amid thunderous noise and splashing turbulence, which in most cases no one hears or sees. They exist only a short time and then slowly waste away just a unnoticed.

    Objects of sheerest beauty, they have been called. Appearing in an andless variety of shapes they may be dazzlingly white, or they may be glassy blue, green, or purple, tinted faintly or in darker hues. They are graceful, stately, inspiring-in calm, sunlit seas.

    But they are also called frightening and dangerous, and that they are-in the night, in the fog, and in storms. Even in clear weather one is wise to stay a safe distance away from them. Most of their bulk is hidden below the water, so their underwater parts may extend out far beyond the visible top. Also, they may roll over uexpectedly, churning the waters around them.

    Icebergs are parts of glaciers that break off, drift into the water, float about awhile, and finally melt. Icebergs afloat today are made of snowflakes that have fallen over long ages of time. They embody snows that drifted down hundreds, or many thousands, or in some cases maybe a milliom years ago. The snows fell in polar regions and on cold mountains, where they melted only a little or not at all, and so collected to great depths over the years and centuries.

    As each year’s snow accumulation lay on the surface, evaporation and melting caused the snowflakes slowly to lose their feathery points and become tiny grains of ice. When new snow fell on top of the old, it too turned to icy grains. So blankets of snow and ice grains mounted layer upon layer and were of such great thickness that the weight of the upper layers compressed the lower ones. With time and pressure from above, the many small ice grains joined and changed to larger crystals, and eventually the deeper crystals merged into a solid mass of ice.

The invention of the incandescent light bulb by Thomas A. Edison in 1879 created a demand for a cheap, readily available fuel with which to generate large amounts of electric power. Coal seemed to fit the bill, and it fueled the earliest power stations (which were set up at the end Of the nineteenth century by Edison himself). As more power plants were constructed throughout the country, the reliance on coal increased. Since the First World War, coal-fired power plants have accounted for about half of the electricity produced in the United States each year. In 1986 such plants had a combined generating capacity of 289,000 megawatts and consumed 33 percent of the nearly 900 million tons of coal mined in the country that year. Given the uncertainty in the future growth of nuclear power and in the supply of oil and natural gas, coal-fired power plants could well provide up to 70 percent of the electric power in the United States by the end of the century.

Yet, in spite of the fact that coal has long been a source of electricity and may remain one for many years (coal represents about 80 percent of United States fossil-fuel reserves), it has actually never been the most desirable fossil fuel for power plants. Coal contains less energy per unit of weight than natural gas or oil; it is difficult to transport, and it is associated with a host of environmental issues, among them acid rain. Since the late 1960's problems of emission control and waste disposal have sharply reduced the appeal of coal-fired power plants. The cost of ameliorating these environmental problems, along with the rising cost of building a facility as large and complex as a coal-fired power plant, has also made such plants less attractive from a purely economic perspective.

Changes in the technological base of coal fired power plants could restore their attractiveness, however. Whereas some of these changes are evolutionary and are intended mainly to increase the productivity of existing plants, completely new technologies for burning coal cleanly are also being developed.

Born in 1830 in rural Amherst, Massachusetts, Emily Dickinson spent her entire life in the household of her parents. Between 1858 and 1862, it was later discovered, she wrote like a person possessed, often producing a poem a day. It was also during this period that her life was transformed into the myth of Amherst.

Withdrawing more and more, keeping to her room sometimes even refusing to see visitors who called, she began to dress only in white - a habit that added to her reputation as an eccentric.

In their determination to read Dickinson's life in terms of a traditional romantic plot, biographers have missed the unique pattern of her life - her struggle to create a female life not yet imagined by the culture in which she lived. Dickinson was not the innocent, lovelorn and emotionally fragile girl sentimentalized by the Dickinson myth and popularized by William Luce’s 1976 play, The BeIle of Amherst. Her decision to shut the door on Amherst society in the 1950's transformed her house into a kind of magical realm in which she was free to engage her poetic genius. Her seclusion was not the result of a failed love affairs but rather a part of a more general pattern of renunciation through which she, in her quest for self – sovereignty, carried on an argument with the Puritan fathers, attacking with wit and irony their cheerless Calvinist doctrine, their stern patriarchal God, and their rigid notions of "true womanhood."

The first navigational lights in the New World were probably lanterns hung at harbor entrances. The first lighthouse was put up by the Massachusetts Bay Colony In 1766 on Little Brewster Island at the entrance to Boston Harbor. Paid for and maintained by light dues levied on ships, the original beacon was blown up in 1776. By then there were only a dozen or so true lighthouses in the colonies. Little over a century later, there were 700 lighthouses.

 The first eight erected on the West Coast in the 1850’s featured the same basic New England design: a Cape Cod dwelling with the tower rising from the center or standing close by. In New England and elsewhere, though, lighthouses reflected a variety of architectural styles. Since most stations in the Northeast were built on rocky eminences, enormous towers were not the rule. Some were made of stone and brick, others of wood or metal. Some stood on pilings or stilts: some were fastened to rock with iron rods. Farther south, from Maryland through the Florida Keys, the coast was low and sandy. It was often necessary to build tall towers there – massive structures like the majestic Cape Hatteras, North Carolina lighthouse, which was lit in 1870. At 190 feet, it is the tallest brick lighthouse in the country. 

Not withstanding differences in appearance and construction, most American lighthouses shared several features: a light, living quarters, and sometimes a bell (or, later, a foghorn). They also had something else in common: a keeper and, usually, the keeper's family. The keeper's essential task was trimming the lantern Nick in order to maintain a steady bright flame. The earliest keepers came from every walk of life-they were seamen. Farmers, mechanics, rough mill hands-and appointments were often handed out by local customs commissioners as political plums. After the administration of lighthouses was taken over in 1852 by the United States Lighthouse 803rd, an agency of the Treasury Department, the keeper corps gradually became highly professional. 

In the past oysters were raised in much the same way as dirt farmers raised tomatoes - by transplanting them. First, farmers selected the oyster bed, cleared the bottom of old shells and other debris, then scattered clean shells about. Next, they "planted" fertilized oyster eggs, which within two or three weeks hatched into larvae. The larvae drifted until they attached themselves to the clean shells on the bottom. There they remained and in time grew into baby oysters called seed or spat. The spat grew larger by drawing in seawater from which they derived microscopic particles of food. Before long farmers gathered the baby oysters transplanted them in other waters to speed up their growth, then transplanted them once more into another body of water to fatten them up.

Until recently; the supply of wild oysters and those crudely farmed were more than enough to satisfy people's needs. But today the delectable seafood is no longer available in abundance. The problem has become so serious that some oyster beds have vanished entirely.

Fortunately, as far back as the early 1900's marine biologists realized that if new measures were not taken, oysters would become extinct or at best a luxury food. So they set up well equipped hatcheries and went to work. But they did not have the proper equipment or the skill to handle the eggs. They did not know when, what, and how to feed the larvae. And they knew little about the predators that attack and eat baby oysters by the millions. They failed, but they doggedly kept at it. Finally, in the 1940's a significant breakthrough was made.

The marine biologists discovered that by raising the temperature of the water, they could induce oysters to spawn not only in the summer but also in the fall, winter, and spring. Later they developed a technique for feeding the larvae and rearing them to spat. Going still further, they succeeded in breeding new strains that were resistant to diseases, grew faster and larger, and flourished in water of different salinities and temperatures. In addition, the cultivated oysters tasted better.