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。