Since computers were introduced，they（）to be useful tools for people weak in math.-焚题库

Since computers were i

单选题 Since computers were introduced，they（）to be useful tools for people weak in math.

A.had proved

B.have proved

C.will prove

D.are proving

正确答案： B

答案解析: 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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