文章来源：华樱外语 发布时间：2016年12月06日 点击数： 次
Paragraph 1: The story of the westward movement of population in the United States is, in the main, the story of the expansion of American agriculture—of the development of new areas for the raising of livestock and the cultivation of wheat, corn, tobacco, and cotton. After 1815 improved transportation enabled more and more western farmers to escape a self-sufficient way of life and enter a national market economy. During periods when commodity prices were high, the rate of westward migration increased spectacularly. "Old America seemed to be breaking up and moving westward," observed an English visitor in 1817,during the first great wave of migration. Emigration to the West reached a peak in the 1830's. Whereas in 1810 only a seventh of the American people lived west of the Appalachian Mountains, by 1840 more than a third lived there.
1. What is the purpose of the statement, “Whereas in 1810 only a seventh of the American people lived west of the Appalachian Mountains, by 1840 more than a third lived there”?
O To illustrate that generally population shifts occur rapidly
O To correct a mistaken impression of American agriculture from 1810 to 1840
O To emphasize the range and speed with which the westward migration occurred
O To demonstrated how attractive the Appalachian Mountains were to Americans
Paragraph 2: Pollen samples from freshwater lakes in Syria and elsewhere tell us forest cover expanded rapidly at the end of the Ice Age, for the southwestern Asian climate was still cooler and considerably wetter than today. Many areas were richer in animal and plant species than they are now, making them highly favorable for human occupation. About 9000 B.C., most human settlements lay in the area along the Mediterranean coast and in the Zagros Mountains of Iran and their foothills. Some local areas, like the Jordan River valley, the middle Euphrates valley, and some Zagros valleys, were more densely populated than elsewhere. Here more sedentary and more complex societies flourished. These people exploited the landscape intensively, foraging on hill slopes for wild cereal grasses and nuts, while hunting gazelle and other game on grassy lowlands and in river valleys. Their settlements contain exotic objects such as seashells, stone bowls, and artifacts made of obsidian (volcanic glass), all traded from afar. This considerable volume of intercommunity exchange brought a degree of social complexity in its wake.
1. Why does the author mention "seashells, stone bowls, and artifacts made of obsidian"?
O To give examples of objects obtained through trade with other societies
O To illustrate the kinds of objects that are preserved in a cool climate
O To provide evidence that the organization of work was specialized
O To give examples of the artistic ability of local populations
Paragraph 1: When one considers the many ways by which organisms are completely destroyed after death, it is remarkable that fossils are as common as they are. Attack by scavengers and bacteria, chemical decay, and destruction by erosion and other geologic agencies make the odds against preservation very high. However, the chances of escaping complete destruction are vastly improved if the organism happens to have a mineralized skeleton and dies in a place where it can be quickly buried by sediment. Both of these conditions are often found on the ocean floors, where shelled invertebrates (organisms without spines) flourish and are covered by the continuous rain of sedimentary particles. Although most fossils are found in marine sedimentary rocks, they also are found in terrestrial deposits left by streams and lakes. On occasion, animals and plants have been preserved after becoming immersed in tar or quicksand, trapped in ice or lava flows, or engulfed by rapid falls of volcanic ash.
1. In paragraph 1, what is the author's purpose in providing examples of how organisms are destroyed?
O To emphasize how surprising it is that so many fossils exist
O To introduce a new geologic theory of fossil preservation
O To explain why the fossil record until now has remained incomplete
O To compare how fossils form on land and in water
Paragraph 2: The term "fossil" often implies petrifaction, literally a transformation into stone. After the death of an organism, the soft tissue is ordinarily consumed by scavengers and bacteria. The empty shell of a snail or clam may be left behind, and if it is sufficiently durable and resistant to dissolution, it may remain basically unchanged for a long period of time. Indeed, unaltered shells of marine invertebrates are known from deposits over 100 million years old. In many marine creatures, however, the skeleton is composed of a mineral variety of calcium carbonate called aragonite. Although aragonite has the same composition as the more familiar mineral known as calcite, it has a different crystal form, is relatively unstable, and in time changes to the more stable calcite.
2. Why does the author mention "aragonite" in the passage?
O To emphasize that some fossils remain unaltered for millions of years
O To contrast fossil formation in organisms with soft tissue and in organisms with hard shells
O To explain that some marine organisms must undergo chemical changes in order to fossilize
O To explain why fossil shells are more likely to survive than are fossil skeletons