问题

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

正确答案是：

同类题型

．—______ I lock the lab before I go home?—Don’t bother．I’ll check it myself later．

下列各句中，没有语病的一句是（）

The Diof Taiwan.

It’s dark in the room. Why not ______ the light

_______,when Marx was already _______,he found it was important to study the situation in Russia, so he began to learn Russian.