单项选择题

There are two factors which determine an individual’s intelligence. The first is the sort of brain he is born【C1】______.Human brains differ considerably, 【C2】______being more capable than others. 【C3】______no matter how good a brain he has to begin with, an individual will have a low order of intelligence【C4】______has opportunities to learn. So the second factor is what. 【C5】______to the individual—the sort of environment in which he is brought【C6】______.If an individual is handicapped(受阻碍) 【C7】______,it is likely that his brain will【C8】______to develop and he will【C9】______attain the level of intelligence of which he is【C10】______. The importance of environment in determining an individual’s intelligence can be【C11】______by the case history of the identical twins, Peter and John. When the twins were three months old their parents died, and they were placed in【C12】______foster(寄养)homes. Peter was reared by parents of low intelligence in an【C13】______community with poor educational【C14】______that was offered to them. John【C15】______, was educated in the home of well-to-do parents who had been to college. This environment【C16】______continued until the twins were【C17】______their late teens as young adults, 【C18】______they were given tests to【C19】______their intelligence. John’s I.Q. was 125, twenty-five points higher than the【C20】______and fully forty points higher than his identical brother. 【C2】