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Economics,severalcoursesofwhichIhavetakenthusfar,tobedifficultbutusefulforalmostallstudents.A.proveB.provesC.havebeenprovedD.areproved

题目详情
Economics,several courses of which I have taken thus far,____ to be difficult but useful for almost all students.
A.prove B.proves C.have been proved D.are proved
▼优质解答
答案和解析
Economics 是单数
prove用法特殊,没有被动的