四六级阅读的每日一练：第4篇

　　None of the scientists had X-ray eyes: they had no 14 powers for looking down below the earths surface. They were 15 putting to use one of the newest methods of 16 minerals in the groundusing 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