【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 can be inferred from paragraph 1 about western farmers prior to 1815?
A.They had limited their crop production to wheat, corn, tobacco, and cotton.
B. They were able to sell their produce at high prices.
C. They had not been successful in raising cattle.
D. They did not operate in a national market economy.
本题中有非常明显的信息可以帮助我们定位，即年份数字“1815”，定位到原文After 1815 improved transportation enabled more and more western farmers to escape a self-sufficient way of life and enter a national market economy. 在1815年之后，改进的交通方式使得越来越多的西部弄明逃开了自给自足的生活方式，进入了*市场经济。这是讲在1815年之后的事情，而题干中问的是“prior to 1815”，即在1815年之前，那么根据反向推理原理，直接对1815年之后的事情取反，即“在1815年之前，交通方式还未改进，人们是自给自足的生活方式，还未进入*市场经济”，直接对应D选项。所以本题选择D选项。
【Paragraph 1】It was not until the Cambrian period, beginning about 600 million years ago, that a great proliferation of macroscopic species occurred on Earth and produced a fossil record that allows us to track the rise and fall of biodiversity. Since the Cambrian period, biodiversity has generally risen, but there have been some notable exceptions. Biodiversity collapsed dramatically during at least five periods because of mass extinctions around the globe. The five major mass extinctions receive most of the attention, but they are only one end of a spectrum of extinction events. Collectively, more species went extinct during smaller events that were less dramatic but more frequent. The best known of the five major extinction events, the one that saw the demise of the dinosaurs, is the Cretaceous-Tertiary extinction.
2. Paragraph 1 supports which of the following statements about life on Earth before the Cambrian period?
A. Biodiversity levels were steady, as indicated by the fossil record.
B. Levels of biodiversity could not be tracked.
C. The most dramatic extinction episode occurred.
D. Few microscopic species existed.
本题中我们可以根据专业词汇“Cambrian period”定位到It was not until the Cambrian period, beginning about 600 million years ago, that a great proliferation of macroscopic species occurred on Earth and produced a fossil record that allows us to track the rise and fall of biodiversity. 直到六亿年前的寒武纪时期，肉眼可见的生物才在地球上大量出现并产生可以让我们了解物种多样性兴衰的化石。可是题干中用的是“before the Cambrian period”，即寒武纪之前，那么只要将原文中寒武纪之后的内容取反，即“在寒武纪之前，肉眼可见的生物还没有大量出现，我们还不能了解物种的多样性”，对应B选项。