Question

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

1. A.
   asked
2. B.
   ask
3. C.
   being asked
4. D.
   having asked

Answer 1

A
试题分析：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。
考点：考查非谓语动词的省略。
点评：状语从句的省略同时具备下列两个条件:①主句和从句的主语一致，或从句主语为it；②从句主要动词是be的某种形式。从句中的主语和be动词常可省略