Question

I won’t tell the students 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：

由主句的一般将来时态排除D项；再由until引导的时间状语从句排除B、C项(在时间状语从句中用一般现在时态代替一般将来时态，但在强调动作完成时可以用现在完成时态)；从句的for more than an hour表明是一直延续的动作，所以用完成进行时态。整句意思为：直到学生一直演算这道数学题达一个多小时之后，我才会告诉学生答案。