Being a teacher always encouraging students to think for themselves I won't tell them ans

问题补充：

Being a teacher always encouraging students to think for themselves, I won 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

答案：

(答案→)A. have worked

B. will have worked

C. will have been working

D. had worked

解析：考查时态：句意：做老师总是鼓励学生独立思考，直到他们这道数学题算了一个多小时我才告诉他们答案。主句是一般将来时，从句用一般现在时或现在完成时代替将来时，或将来完成时。选A。