When how old he was he kept silent.A. askingB. askedC. to be askedD. ask

问题补充：

When how old he was, he kept silent.

A. asking

B. asked

C. to be asked

D. ask

答案：

A. asking

(答案→)B. asked

C. to be asked

D. ask

解析：考查非谓语动词。句意：当被问到多大了的时候，他保持沉默。he与ask是动宾关系，应该用过去分词，排除A、D；C项表示将来，与题意不符。故选B。