There is no doubt that he is a good professorhe is doing fine.A. butB. becauseC. soD. yet

问题补充：

There is no doubt that he is a good professorhe is doing fine.

A. but

B. because

C. so

D. yet

答案：

A. but

(答案→)B. because

C. so

D. yet

解析：because引导原因状语从句，意思是：他干得很好。