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

答案：A
解析：

考查动词的时态。句意为“直到这个学生在这个数学问题上思考一个多小时，我才告诉他答案”。当主句用一般将来时，时间状语从句可以用现在时态或现在完成时态。根据后面的“for more than an hour”可知动作持续了一段时间而且一直在进行，应该用现在完成进行时。