Question

Being a teacher always encouraging students to think for themselves, I won't tell them answers until they __________ on a math problem for more than an hour.

A．have worked	B．will have worked
C．will have been working	D．had worked

Answer 1

A

試題分析：考查時態(tài)：句意：做老師總是鼓勵學生獨立思考，直到他們這道數(shù)學題算了一個多小時我才告訴他們答案。主句是一般將來時，從句用一般現(xiàn)在時或現(xiàn)在完成時代替將來時，或?qū)�來完成時。選A。
點評：這題考查的是時間條件狀語從句的時態(tài)問題，此類的狀語從句不能用將來時，用一般現(xiàn)在時或現(xiàn)在完成時代替將來時，或?qū)�來完成時。