C符合题意。 

Passage Three

Questions 11 to 15 are based on the following passage.

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

The importance of environment in determining an individual’s intelligence can be demonstrated by the case history of the identical twins, Peter and Mark. Being identical, the twins had identical brains at birth, and their growth processes were the same. When the twins were three months old, th