根据下面内容，回答176-180题There are two factors which determine an individual's intelligence．The first is the sort ofbrain he is born with．Human brains differ considerably, some being more capable than others．Butno matter how good a brain he has to begin with, an individual will have a low order of intelli-gence 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 environmentally,it is likely that his brain will fail to develop and he will never attain the level of intelligence ofwhich he is capable.The importance of environment in determining an individual's intelligence can be demonstrat-ed by the case history of the identical twins, Peter and Mark．Being identical, the twins had iden-tical brains at birth, and their growth processes were the same．When the twins were three monthsold, their parents died, and they were placed in separate foster homes．Peter was raised by parentsof low intelligence in an isolated community with poor educational opportunities．Mark was rearedin the home of well-to-do parents who had been to college．He was read to as a child, sent to goodschools, and given every opportunity to be Stimulated intellectually．This environmental differencecontinued until the twins were in their late teens, when they were given tests to measure their in-telligence．Mark's I.Q．was 125, twenty-five points higher than the average and fully forty pointshigher than his identical brother．Given equal opportunities, the twins, having identical brains,would have tested at roughly the same level. This passage suggests that an individual's I.Q（）

A. can be predicted at birth
B. stays the same throughout his life
C. can be increased by education
D. is determined by his childhood