31. The author says that the world population is growing because _____.

　　A) there are many rich valleys and fertile plains

　　B) the pattern of distribution is being altered

　　C) people are living longer

　　D) new land is being brought under cultivation

　　32. The author says that in densely populated areas the land might be more productively farmed if _____.

　　A) the plots were subdivided

　　B) a large part of the people moved to a different part of the country

　　C) industrial methods were used in farming

　　D) the units of land were made much larger

　　33. We are told that there are now farms beyond the Arctic Circle. This has been made possible by _____.

　　A) producing new strains of crops

　　B) irrigation and dry-farming methods

　　C) providing fertilizers

　　D) destroying pests and disease

　　34. Which of these words is nearest in meaning to the word "strains"?

　　A) types B) sizes

　　C) seeds D) harvests

　　35. The author's main purpose is to _____.

　　A) argue for a belief B) describe a phenomenon

　　C) entertain D) propose a conclusion

　　Passage Four

　　Questions 36 to 40 are based on the following passage.

　　For some time past it has been widely accepted that babies-and other creatures-learn to do things because certain acts lead to "rewards"; and there is no reason to doubt that this is true. But it used also to be widely believed that effective rewards, at least in the early stages, had to be directly related to such basic physiological(生理的) "drives" as thirst or hunger. In other words, a baby would learn if he got food or drink or some sort of physical comfort, not otherwise.

　　It is now clear that this is not so. Babies will learn to behave in ways that produce results in the world with no reward except the successful outcome.

　　Papousek began his studies by using milk in the normal way to "reward" the babies and so teach them to carry out some simple movements, such as turning the head to one side or the other. Then he noticed that a baby who had had enough to drink would refuse the milk but would still go on making the learned response with clear signs of pleasure. So he began to study the children's responses in situations where no milk was provided. He quickly found that children as young as four months would learn to turn their heads to right or left if the movement "switched on" a display of lights-and indeed that they were capable of learning quite complex turns to bring about this result, for instance, two left or two right, or even to make as many as three turns to one side.

　　Papousek's light display was placed directly in front of the babies and he made the interesting observation that sometimes they would not turn back to watch the lights closely although they would "smile and bubble" when the display came on. Papousek concluded that it was not primarily the sight of the lights which pleased them, it was the success they were achieving in solving the problem, in mastering the skill, and that there exists a fundamental human urge to make sense of the world and bring it under intentional control.

　　36. According to the author, babies learn to do things which .

　　A) are directly related to pleasure

　　B) will meet their physical needs

　　C) will bring them a feeling of success

　　D) will satisfy their curiosity