比如题目“Paragraph 3 supports the idea that Gause’s experiments were important because they ____”题干问的是文章支持Gause的实验很重要是因为什么?由人名Gause定位到红字部分，发现本句和“important ”没有关系，但是从下一句可以看出实验证明了”the law of competitive exclusion”，解出题目。
Paragraph 3: To what extent competition determines the composition of a community and the density of particular species has been the source of considerable controversy. The problem is that competition ordinarily cannot be observed directly but must be inferred from the spread or increase of one species and the concurrent reduction or disappearance of another species. The Russian biologist G. F. Gause performed numerous two-species experiments in the laboratory, in which one of the species became extinct when only a single kind of resource was available. On the basis of these experiments and of field observations, the so-called law of competitive exclusion was formulated,according to which no two species can occupy the same niche. Numerous seeming exceptions to this law have since been found, but they can usually be explained as cases in which the two species, even though competing for a major joint resource, did not really occupy exactly the same niche. (TPO 29 Competition)
例题：As railroad lines fanned out from Chicago, farmers began to acquire open prairie land in Illinois and then Iowa, putting the fertile, deep black soil into production. Commercial agriculture transformed this remarkable treeless environment. To settlers accustomed to eastern woodlands, the thousands of square miles of tall grass were an awesome sight. Indian grass, Canada wild rye, and native big blue stem all grew higher than a person. Because eastern plows could not penetrate the densely tangled roots of prairie grass, the earliest settlers erected farms along the boundary separating the forest from the prairie. In 1837, however,John Deere patented a sharp-cutting steel plow that sliced through the sod without soil sticking to the blade. Cyrus McCormick refined a mechanical reaper that harvested fourteen times more wheat with the same amount of labor. By the1850s McCormick was selling 1,000 reapers a year and could not keep up with demand, while Deere turned out 10,000 plows annually. (TPO 33 Railroads and Commercial Agriculture in Nineteenth-Century United States)
According to paragraph 5, the first settlers generally did not farm open prairie land because _____
A.they could not plow it effectively with the tools that were available.
B.prairie land was usually very expensive to buy.
C.the soil along boundaries between the forest and the prairie was more fertile than the soil of the open prairie.
D.the railroad lines had not yet reached the open prairie when the first settlers arrived.
根据题干中“the first settlers”和“the first settlers”大致定位到第一句和第三句这样的语义群，再根据题干中的“ because”定位到第四句。(eastern plows could not penetrate the densely tangled roots of prairie grass)。
看选项：A选项提到了耕作工具的原因;B选项出现了原文中没有的信息，排除;C选项中出现了原文中不存在的对比关系，根据第一句可以看出the soil of the open prairie是肥沃的，但是没有对比;D选项并非定位到的内容，排除。所以正确选项是A选项。