Some homing pigeon experts claim that this bird is gifted with a form of built-in radar that helps it find its own loft after hours of flight, for hidden under the head feathers are two very sensitive ears, while the sharp, prominent eyes can see great distances in daytime.

　　Why do homing pigeons fly home? They are not unique in this inherent skill; it is found in most migratory birds, in bees, ants, toads, and even turtles, which have been known to travel hundreds of miles to return to their homes. But in the animal world, the homing pigeon alone can be trusted with its freedom and trained to carry out the missions that people demand.

　　21. This passage is mainly about_______.

　　A. homing pigeons and their training

　　B. how to buy a homing pigeon

　　C. protection of homing pigeons against the threat of extinction

　　D. liberation of homing pigeons

　　22. According to the passage, what happens to homing pigeons when they are about a month old?

　　A. They are kept in a trap.

　　B. They enter their first race.

　　C. They begin a training program.

　　D. They get their wings clipped and marked.

　　23. According to the passage, the difference between a homing pigeon and an ordinary one is_______.

　　A. the span of the wings B. the shape of the eyes

　　C. the texture of the feathers D. the size of the brain

　　24. The author mentions all of the following attributes that enable a homing pigeon to　return home EXCEPT_______.

　　A. instinct B. air sacs

　　C. sensitive ears D. good eyes

　　25. Why does the author mention bees, ants, toads, and turtles in the last paragraph?

　　A. To describe some unusual kinds of pets.

　　B. To measure distances traveled by various animals.

　　C. To compare their home-finding abilities with those of homing pigeons.

　　D. To interest the reader in learning about other animals.

　　21. A 22. C 23. D 24. B 25. C

　　Are some people born clever, and others born stupid? Or is intelligence developed by our environment and our experiences? Strangely enough, the answer to both these questions is yes. To some extent our intelligence is given us at birth, and no amount of special 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 rich and varied surroundings. Thus the limits of a person's intelligence are fixed at birth, but 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(任意的) from the population,

　　it is likely that their degrees of intelligence will be completely different. If on the other hand we take two identical (完全相同的) 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 likely to have similar degrees of intelligence.

　　26. Which of these sentences best describes the writer's point in Paragraph 1?

　　A. To some extent, intelligence is given at birth.

　　B. Intelligence is developed by the environment.

　　C. Some people are born clever and others born stupid.

　　D. Intelligence is fixed at birth, but is developed by the environment.

　　27. It is suggested in this passage that_______.

　　A. unrelated people are not likely to have different intelligence

　　B. close relations usually have similar intelligence

　　C. the closer the blood relationship between people, the more different they are likely to be in intelligence

　　D. people who live in close contact with each other are not likely to have similar degrees of intelligence

　　28. Brothers and sisters are likely to_______.

　　A. have similar intelligence B. have different intelligence

　　C. go to the same university D. go to the same factory

　　29. In Paragraph 1, the word "surroundings" means_______.

　　A. intelligence B. life

　　C. environments D. housing

　　30. The best title for this article would be_______.

　　A. On Intelligence

　　B. What Intelligence Means

　　C. We Are Born with Intelligence

　　D. Environment Plays a Part in Developing Intelligence

　　26. D 27. B 28. A 29. C 30. A