12．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 envionmentally，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 intellingence 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，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 well-to-do 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 enviromental difference continued until the twins were in their late teens，when they were given tesets to measure their intelligence．Mark's I．Q．was 125，twenty-five 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．
28．This selection can best be titledB．
A．Measuring Your Intelligence
B．Intelligence and Environment
C．The Case of Peter and Mark
D．How the brain Influences Intelligence
29．According to the passage，the average I．Q．isB．
A.85 B.100 C.110 D.125
30．The case history of the twins appears to support the conclusion thatC．
A．individual with identical brains seldom test at same level
B．an individual's intelligence is determined only by his enviroment
C．lack of opportunity blocks the growth of intelligence
D．changes of enviroment produce changes in the structure of the brain．
分析 本文讲述了关于智力发展的因素．第一个是先天性的因素，第二个也是更重要的一个因素就是环境因素．文章根据双胞胎的案例，说明了缺乏受教育的机会会阻碍了智力的增长．可见环境对于智力发展的影响很大．
解答 28-30．BBC
28．B 考查文章主旨．根据"The importance of environment in determining an individual's intellingence"可知，本文要讲述的是环境在决定个人的智力方面的重要性．故选B．
29．B 考查细节理解．根据"Mark's I．Q．was 125，twenty-five points higher than the average"可知，对于125的IQ成绩来说，是高于平均IQ25分，可计算出平均IQ应当是100．故选B．
30．C 考查推理判断．根据双胞胎的案例可知，缺乏受教育的机会会阻碍了智力的增长．故选C．
点评 阅读理解考察学生的细节理解和推理判断能力，做细节理解题时一定要找到文章中的原句，和题干进行比较，再做出正确的选择．在做推理判断题不要以个人的主观想象代替文章的事实，要根据文章事实进行合乎逻辑的推理判断．
