We still cannot persuade him to give up smoking hard we tried.A. soB. howC. thoughD. howe

问题补充：

We still cannot persuade him to give up smoking hard we tried.

A. so

B. how

C. though

D. however

答案：

A. so

B. how

C. though

(答案→)D. however

解析：本题考查however引导的让步状语从句。however引导的让步状语从句后面直接接形容词或副词。so和though则不可以。