首先，因果关系词，其实有两类，一个是表示原因的：as、since、thanks to、as result of、because of、owing to、result from、due to、on account of、by virtue of、in that、attribute to；另一个是表示结果的：as a consequence、thus、hence、so、as a result、result in、contribute to、lead to、cause、breed、trigger
The extreme seriousness of desertification results from the vast areas of land and the tremendous numbers of people affected, as well as from the great difficulty of reversing or even slowing the process.
A Desertification is a significant problem because it is so hard to reverse and affects large areas of land and great numbers of people.
B Slowing down the process of desertification is difficult because of population growth that has spread over large areas of land.
C The spread of deserts is considered a very serious problem that can be solved only if large numbers of people in various countries are involved in the effort.
D Desertification is extremely hard to reverse unless the population is reduced in the vast areas affected.
1.找出句子的主谓宾，也就是谁做了什么，然后关注句子的逻辑关系。例题的主语是：seriousness of desertification，逻辑关系词是表示原因的：result from，所以我们可以优先看有表示原因的选项，他们中若有正确答案，那么剩下的选项就无需过问了。这样做不仅快，而且效率高。我们不难发现：A选项中有because；B选项中有because of；所以我们先看这两个选项。
2.我们还发现原因用as well as相连，说明是两个原因，一个是影响land和people，一个是reverse和slow the process很难。A选项正确表达了句意，而B选项把原文中并列的两个原因变成了因果关系，很明显是错的。
Paragraph 4: So, in another set of experiments, Kramer put identical food boxes around the cage, with food in only one of the boxes. The boxes were stationary, and the one containing food was always at the same point of the compass. However, its position with respect to the surroundings could be changed by revolving either the inner cage containing the birds or the outer walls, which served as the background. As long as the birds could see the Sun, no matter how their surroundings were altered, they went directly to the correct food box. Whether the box appeared in front of the right wall or the left wall, they showed no signs of confusion. On overcast days, however, the birds were disoriented and had trouble locating their food box.
Which of the following can be inferred from paragraph 4 about Kramer’s reason for filling one food box and leaving the rest empty?
A He believed the birds would eat food from only one box.
B He wanted to see whether the Sun alone controlled the birds' ability to navigate toward the box with food.
C He thought that if all the boxes contained food, this would distract the birds from following their migratory route.
D He needed to test whether the birds preferred having the food at any particular point of the compass.
首先，我们来明确一下推断的定义（infer, imply, indicate），纵使它是推断题，也不是意味着这题是主观臆断，臆想或是联想得出的。这道题也是要通过提取题干中的关键词到文章中的明确位置，然后文中没有平铺直叙地告诉你答案，需要我们根据一些线索找到答案。
接下来我们来看一下这道题，题干中出现Kramer, filling one food box and leaving the rest empty定位在第四段句：with food in only one of the boxes，而解开这道题的重点就在于：reason。我们看到句话一开始说到，so, in another set of experiments，很明显，答案并不在这一段，而是上一段的最后。所以答案是B。
Paragraph 6: ■Because they are always swimming, tunas simply have to open their mouths and water is forced in and over their gills. ■Accordingly, they have lost most of the muscles that other fishes use to suck in water and push it past the gills. ■In fact, tunas must swim to breathe. ■They must also keep swimming to keep from sinking, since most have largely or completely lost the swim bladder, the gas-filled sac that helps most other fish remain buoyant.
Look at the four squares [█] that indicate where the following sentence could be added to the passage.
Consequently, tunas do not need to suck in water.
Where would the sentence best fit?