Iwon’ttellthestudenttheanswertothemathproblemuntilhe  ...

問題詳情：

 I won’t tell the student the answer to the math problem until he        on it for more than an hour.

A. has been working                       B. will have worked   

C. will have been working                  D. had worked                              

【回答】

A

知識點：現在完成進行時及其被動式

題型：選擇題