【題目】People ____ more and more useful things to protect the earth since Earth Day was started.

A. did B. were doing

C. will do D. have done

【答案】D

【解析】

試題分析：句意：人們已經(jīng)做了越來越多的有用的事情來保護我們的地球，自從地球日建立起。根據(jù)since引導(dǎo)的時間狀語從句可知用現(xiàn)在完成時have done的結(jié)構(gòu)；結(jié)合句意，故選D

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