Since computers were introduced, they_________tobe useful tools for people weak in math.
- A.had proved
- B.have proved
- C.will prove
- D.are proving
正确答案及解析
正确答案
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。
Since computers were introduced, they_________tobe useful tools for people weak in math.
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。
