Question

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

Answer 1

A

解析:

现在完成进行时表示动作或状态从过去的某个时候发生或存在，一直延续到现在，并可能继续延续下去。根据后面的“for more than an hour”可知动作持续一段时间而且一直在进行，应该用现在完成进行时。