21. 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

　　22. 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 crucial in determining a person's intelligence

　　D. persons having identical brains will have roughly the same intelligence

　　23. According to the passage, the average I. Q. is_______.

　　A. 85 . B. 100

　　C. 110 D. 125

　　24. The case history of the twins appears to support the conclusion that_______.

　　A. individuals with identical brains seldom test at the 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

　　25. 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

　　答案：21. B 22. C 23. B 24. C 25. C

　　Flying over a desert area in an airplane, two scientists looked down with trained eyes at trees and bushes. After an hour's 11 one of the scientists wrote in his book, "Look here for 12 metal. " Scientists in another airplane, flying over a mountain region, sent a 13 to other scientists on the ground, "Gold possible. " Walking across hilly ground, four scientists reported, "This ground should be searched for metals. " From an airplane over a hilly wasteland a scientist sent back by radio one word, "Uranium. "

　　None of the scientists had X-ray eyes: they had no 14 powers for looking down below the earth's surface. They were 15 putting to use one of the newest methods of 16 minerals in the ground—using trees and plants as 17 that certain minerals may lie beneath the ground on which the trees and plants are growing.

　　This newest method of searching for minerals is 18 on the fact that minerals deep in the earth may 19 the kind of bushes and trees that grow on the surface.

　　At Watson Bar Creek, a brook six thousand feet high in the mountains of British Columbia, Canada, a mineral search group gathered bags of tree seeds. Boxes were filled with small branches from the trees. Roots were dug and put into boxes. Each bag and box was 20 marked. In a scientific laboratory the parts of the forest trees were burned to ashes and tested. Each small part was examined to learn whether there were minerals in it.

　　A. signs

　　B. sufficiently

　　C. locating

　　D. affect

　　E. merely

　　F. magic

　　G. hints

　　H. carefully

　　I. finding

　　J. message

　　K. flight

　　L. probable

　　M. revealing

　　N. based

　　O. information

　　答案：11. K 12. L 13. J 14. F 15. E 16. C 17. A 18. N 19. D 20. H