Question

(2006·湖北)

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：

主句为一般将来时态，时间状语从句需用一般现在时或现在完成时，因此选A。