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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 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 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 fully forty points higher than his identical brother.
Given equal opportunities, the twins, having identical brains, would have tested at roughly the same level.
1. 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
2. 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
3. According to the passage, the average I. Q.is________.
A. 85
B. 100
C. 110
D. 125
4. The case history of the twins appears to support the conclusion that________.
A. individual with identical brains seldom test at same level
B. an individual's intelligence is determined only by his environment
C. lack of opportunity blocks the growth of intelligence
D. changes of environment produce changes in the structure of the brain
5. 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