Iwon’ttellthestudenttheanswertothemathproblemuntilhe

问题详情：

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. would have worked D. had worked

【回答】

B

知识点：动词时态与语态

题型：选择题