A、The part that birth plays. B、The importance of their positions. C、The importance of their intelligence. D、The role of environm

Are some people born clever, and others born stupid? Or is intelligence developed by our environment and our experience? Strangely enough, the answers to these questions are yes. To some extent, our intelligence is given to us at birth, and no amount of education can make a genius out of a child born with low intelligence. On the other hand, a child who lives in a boring environment will develop his intelligence less than one who lives in the rich and varied surroundings. Thus the limits of a person’s intelligence are fixed at birth, whether or not he reaches those limits will depend on his environment. This view, now held by most experts, can be supported in a number of ways.
    It is easy to show that intelligence is to some extent something we are born with. The closer the blood relationship between two people, the closer they are likely to be in intelligence. Thus if we take two unrelated people at random from population, it is likely that their degree of intelligence will be completely different. If, on the other hand, we take two identical twins, they will very likely be as intelligent as each other. Relations like brothers and sisters, parents and children, usually have similar intelligence, and this clearly suggests that intelligence depends on birth.
    Imagine now that we take two identical twins and put them in different environments. We might send one, for example, to a university and the other to a factory where the work is boring. We would soon find differences in intelligence developing, and this indicates that environment as well as birth plays a part. This conclusion is also suggested by the fact that people who live in close contact with each other, but who are not related at all are all likely to have a similar degree of intelligence.
Questions 19 to 21 are based on the passage you have just heard.
19. Which view about man’s intelligence is the speaker in favour of?
20. What can a child do if he is born with low intelligence?
21. What does the example of the twins going to a university and to a factory separately show?