Unless by the police you should keep silent over the accident.A. asked B. ask C. being a

问题补充：

Unless by the police, you should keep silent over the accident.

A. asked

B. ask

C. being asked

D. having asked

答案：

(答案→)A. asked

B. ask

C. being asked

D. having asked

解析：从by the police可以说明you与ask之间构成被动关系，故排除ＢＤ，另外非谓语动词的省略往往会省略从句的主语和部分谓语，即be动词，故选答案Ａ，也可以将状语从句补全，即Unless you are asked by the police,然后再去掉you are,即可得知答案。