26. Statuses are marvellous human inventions that enable us to get along with one another and to determine where we "fit" in society.

27. Most of us, at very high speed, assume the statuses that various situations require.

28. It is, everyone agrees, a huge task that the child performs when he learns to speak and the fact that he does so in so short a period of time challenges explanation.

29. It is agreed, too, that from about three months they play with sounds for enjoyment, and that by six months they are able to add new sounds to their repertoire (能发出的全部声音)。

30. Psychologists take opposing views of how external rewards, from warm praise to cold cash, affect motivation and creativity.

31. But the careful use of small monetary rewards sparks creativity in grade-school children, suggesting that properly presented inducements indeed aid inventiveness, according to a study in the June Journal of Personality and Social Psychology.

32. In earlier grades, the use of so-called token economies, in which students handle challenging problems and receive performance-based points toward valued rewards shows promise in raising effort and creativity, the Delaware psychologist claims.

33. Researchers have established that when people are mentally engaged, biochemical changes occur in the brain that allow it to act more effectively in cognitive areas such as attention and memory.

34. People will be alert and receptive (愿意接受的) if they are faced with information that gets them to think about things they are interested in.

35. Fozard and others say they challenge their brains with different mental skills, both because they enjoy them and because they are sure that their range of activities will help the way their brains work.

36. Gene Cohen, acting director of the same institute, suggests that people in their old age should engage in mental and physical activities individually as well as in groups.

37. Britain almost more than any other country in the world must seriously face the problem of building upwards, that is to say, of accommodating a considerable proportion of its population in high blocks of flats.

38. In the past our own blocks of flats have been associated with the lower-income groups and they have lacked the obvious provisions, such as central heating, constant hot water supply, electrically operated lifts from top to bottom, and so on, as well as such details, important notwithstanding, as easy facilities for disposal of dust and rubbish and storage places for baby carriages on the ground floor, playgrounds for children on the top of the buildings, and drying grounds for washing.

39. We have seen that they now pollute soil, water, and food, that they have the power to make our streams fishless and our gardens and woodlands silent and birdless.

40. Responsible public health officials have pointed out that the biological effects of chemicals are cumulative over long periods of time, and that the danger to the individual may depend on the sum of the exposures received throughout his lifetime.

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