I had the impression she chose her words carefully.A. whichB. whatC. thatD. whether

问题补充：

I had the impression she chose her words carefully.

A. which

B. what

C. that

D. whether

答案：

A. which

B. what

(答案→)C. that

D. whether

解析：句意：我的印象是她选词很注意。这里是that引导的同位语从句，that在从句中不作成分，只起连接的作用，从句不缺成份，其他的连词都有词意，这里从句的意思完整，故选C。