A、Most people are of similar intelligence regardless of background. B、People of the same blood type have similar intelligence. C

Are some people born clever, and others born stupid? Or is the development of intelligence dependent on environment and experience? Strangely enough, the answer to both questions is yes. To some extent, our intelligence is given us at birth. On the other hand,[23]a child who lives in a boring environment will develop his intelligence less than one who lives in rich and varied surroundings.
    It is easy to show that intelligence is something we are born with. The closer the blood relationship between two people, the closer they are likely to be in intelligence. Therefore if we take two unrelated people at random from the population, it is likely that their degree of intelligence will be completely different. If 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 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 development, 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 likely to have a similar degree of intelligence.
23. What degree of intelligence might a child have, if he lives in a rich and varied environment?
24. Why does the speaker say that intelligence depends on birth?
25. What do we learn about unrelated people who live in close contact according to the passage?