Passage 2

　　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

　　Passage 3

　　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 brought up. If an individual is handicapped(不利) 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. 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(抚养) homes. Peter was raised 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.

　　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