There are two aspects which determine an individual's intelligence. The first is the Drain

be is born【C1】______Human brains differ considerably,【C2】______being more able than others.【C3】______no matter how good a brain he has to begin with, an individual will have a low order of intelligence【C4】______he has opportunities to learn. So the second aspect is what【C5】______to the individual--the environment in which he is brought【C6】______. If an individual is handicapped【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, Tom and Mike. When tile twins were three months old, their parents died, and they were placed in【C12】______foster homes. Tom was mated by parents of low intelligence in an【C13】______community with poor educational【C14】______. Mike,【C15】______was educated in the home of well-to-do parents who had been to college, This environmental【C16】______continued until the twins were【C17】______their late teens,【C18】______they were given tests to【C19】______their intelligence. Mike's IQ was 125, twenty-five points higher than the【C20】______and fully forty points higher than his identical brother.

【C1】

A．for

B．by

C．with

D．in