2012年12月英语四级选词填空专项训练二

　　Unit Two

　　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.

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