There are two factors which determine an individual’s intelligence. The first is the sort of brain he is born with. Human brains differ 41 , some being more capable than others. But no matter how good a brain he has to begin with, a (an) 42 will have a low intelligence unless he has opportunities to learn. So the second factor in what happens to the individual is the sort of environment in which he is 43 . If an individual is handicapped environmentally, it is likely that his brain will fail to develop. And he will never 44 the level of intelligence of which he is capable.

The importance of environment in determining an individual’s intelligence can be 45 by the case history of the identical twins, Peter and Mark. Being identical, the twins had identical brain at birth, and their growth processes were the same. When the twins were three months old, their parents died, and they were placed in 46 foster homes. Peter was reared by parents of low intelligence in an isolated community with poor 47 opportunities. Mark was reared in the home of well-to-do parents who had been to college. He was read to as a child, sent to good schools, and given every opportunity to be 48 intellectually. This environmental difference continued until the twins were in their late teens, when they were given tests to 49 their intelligence. Mark’s I.Q. was 125, twenty-five points higher than the 50 , and fully forty points higher than his identical brother. Given equal opportunities, the twins, having identical brains, would have scored at roughly the same level.

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In some countries, students are expected to be quiet and ________ in the classroom.

A) skeptical B) faithful C) obedient D) subsidiary

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It is a long time before scientists could _________ the mystery of the atom.

A) pierce B) penetrate C) pervade D) permeate

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Hurricanes are killer winds, and their ________ power lies in the physical damage they can do.

A) cumulative B) destructive C) turbulent D) prevalent

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