. If to look after luggage for someone else inform the police at once.A. askedB. to askC

问题补充：

. If to look after luggage for someone else, inform the police at once.

A. asked

B. to ask

C. asking

D. having asked

答案：

(答案→)A. asked

B. to ask

C. asking

D. having asked

解析：句意为：如果有人要你替他看管行李，立即联系警察。ask 的主动形式后不能直接跟不定式作宾语，只能跟不定式作宾补，所以可以直接排除 B、C、D 三项。完整的句子应该是If you are asked to look after luggage for someone else,当从句中的主语和主句的主语一致的时候，可以省略从句的主语和be动词，选A。