B

　　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 order 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 reared.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 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 X.Being identical，the twins had identical brains at birth，and their growth processes were the same.When the twins were three months old，their parents died，and they were placed in separate foster homes.Peter was reared by parents of low intelligence in an isolated community with poor educational opportunities.Mark was reared in the home of well­to­do parents who had been to college.He was read to as a child，sent to good schools，and given every 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，twenty­five points higher than the average and fully forty points higher than his identical brother.Given equal opportunities，the twins，having identical brains，would have tested at roughly the same level.

　　40.This selection can best be titled________.

　　A.Measuring Your Intelligence

　　B.Intelligence and Environment

　　C.The Case of Peter and Mark

　　D.How the Brain Influences Intelligence

　　解析　主旨大意題。本文主要討論了智商與環(huán)境之間的關(guān)系，并以一對失去父母的雙胞胎兄弟的實(shí)例加以證明。

　　答案　B

　　41.The best statement of the main idea of this passage is that________.

　　A.human brains differ considerably

　　B.the brain a person is born with is important in determining his intelligence

　　C.environment is vital to determine a person's intelligence

　　D.persons having identical brains will have roughly the same intelligence

　　解析　推理判斷題。雖然人的智商是由兩個(gè)因素決定的。但是本文用大幅篇章說明了環(huán)境的重要性：好的學(xué)習(xí)、教育環(huán)境對于一個(gè)人的智商發(fā)展來說是必不可少的，并以一對失去父母的雙胞胎兄弟的實(shí)例加以證明。

　　答案　C

　　42.According to the passage，the average I.Q.is________.

　　A.85 B.100 C.110 D.125

　　解析　細(xì)節(jié)理解題。由倒數(shù)第二句“Mark's I.Q.was 125，twenty­five points higher than the average”可知選B。

　　答案　B