eir parents died and they were placed in separate foster(抚养)homes. Peter was raised by parents of low intelligence in an isolated community with fewer educational 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 even- opportunity to be stimulated intellectually. This environmental difference continued until the twins were in their late teens, when they were given tests to measure their intelligence. Mark’s I. Q. was 125, twenty-five points higher than the average and forty points higher than his identical brother. Given equal opportunities, the twins, having identical brains, would have tested at roughly the same level.

11. The main idea of this passage is that ______

A. human brains differ completely

B. the brain a person is born with determines his intelligence.

C. environment is crucial in determining a person’s intelligence

D. persons having identical brains will hav