Since computers were introduced, they___

练习题库2022-08-02 44

问题 Since computers were introduced, they_________tobe useful tools for people weak in math.A.had provedB.have provedC.will proveD.are proving

选项 A.had proved
B.have proved
C.will prove
D.are proving

答案 B

解析句意：自电脑问世以后，它们已被证明是一种对数学薄弱的人们有用的工具。since引导的从句中的动词用一般过去时，主句用现在完成时，故选B。

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英语专升本

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