I think hes been drinking Im not completely sure.A. ifB. thoughC. becauseD. while

问题补充：

I think hes been drinking, Im not completely sure.

A. if

B. though

C. because

D. while

答案：

A. if

(答案→)B. though

C. because

D. while

解析：句意：我认为他一直在喝酒，虽然我不完全确定。If如果；though尽管，虽然；because因为；while在……期间。根据题意选B。