He is so busy with the research he has no time left for any other activity.A. whichB. that

问题补充：

He is so busy with the research he has no time left for any other activity.

A. which

B. that

C. why

D. because

答案：

A. which

(答案→)B. that

C. why

D. because

解析：考查so…that…句型：that结果状语从句，句意：他如此忙于研究以至于没时间参加任何活动。选B。