找到1、2位置之间的句子“Water controls the volume of plant matter produced.”。其中the volume of plant matter和the total amount of plant material意思相同，其次由于water的控制作用，确实会导致两个水量不同的地区(desert和forest)产生差别，前后逻辑非常严谨，所以B是正确答案。
2)逻辑词
逻辑词仅仅是为了简(zhuang)洁(bi)而起的一个名字，指的是能够表示句间逻辑关系的那些词，如however、but、therefore、also、then等等。
出现这些逻辑词的时候，代表着插入句的句意和其前句或后句在信息上存在着某种逻辑关系。根据找到的逻辑关系，结合插入句的句意，可以大致推测一下前文或后文的句意，以此作为寻找正确答案的指向性信息。
例题1
Less colorful birds and animals that inhabit the rain forest tend to rely on forms of signaling other than the visual, particularly over long distances. █ The piercing cries of the rhinoceros hornbill characterize the Southeast Asian rain forest, as do the unmistakable calls of the gibbons. █ In densely wooded environments, sound is the best means of communication over distance because in comparison with light, it travels with little impediment from trees and other vegetation. █ In forests, visual signals can be seen only at short distances, where they are not obstructed by trees. █ The male riflebird exploits both of these modes of signaling simultaneously in his courtship display. The sounds made as each wing is opened carry extremely well over distance and advertise his presence widely. The ritualized visual display communicates in close quarters when a female has approached.
There is also the long, rather terrifying call of the male orangutan, which carries over considerable distances to advertise his presence.
句中出现“also”，根据句意，可以推测正确位置之前至少会提到与动物相关的某种特性，所以才会紧跟插入句所说的“also有雄性O动物的call”。发现第二个位置前面提到rhinoceros hornbill的叫声cries和gibbons的喊声calls，那么把插入句放到第二个位置，起到了进一步举例说明的作用，满足了also的关系，前后逻辑严谨。
例题2
Paragraph 1: Of all the physiological differences in human sleep compared with wakefulness that have been discovered in the last decade, changes in respiratory control are most dramatic. Not only are there differences in the level of the functioning of respiratory systems, there are even changes in how they function. Movements of the rib cage for breathing are reduced during sleep, making the contractions of the diaphragm more important. █ Yet because of the physics of lying down, the stomach applies weight against the diaphragm and makes it more difficult for the diaphragm to do its job. █ However, there are many other changes that affect respiration when asleep.
Paragraph 2: █ During wakefulness, breathing is controlled by two interacting systems. █The first is an automatic, metabolic system whose control is centered in the brain stem. It subconsciously adjusts breathing rate and depth in order to regulate the levels of carbon dioxide (CO2) and oxygen (O2), and the acid-base ratio in the blood. The second system is the voluntary, behavioral system. Its control center is based in the forebrain, and it regulates breathing for use in speech, singing, sighing, and so on. It is capable of ignoring or overriding the automatic, metabolic system and produces an irregular pattern of breathing.
To better understand breathing during sleep, it is, however, helpful to first understand how respiration works in general.
题目出现however，表示本句为转折句。转折句出现表示前后文应该出现论述重点的不同，较多出现的情况为后文反驳前文，较少出现的情况也会表示后文开始论述与前文不完全相同的另一个内容。
根据插入句的句意“然而，为了更好理解睡眠中的呼吸，先搞清楚平时是如何呼吸是很有帮助的”，可以推断出本句具有明显的承上启下的作用，承接上文论述的“睡眠中的呼吸”，引起下文所述的“平时是如何呼吸的”。根据推断寻找后，发现C位置符合承上启下的关系，即为正确答案。