When___the reason for their success,the kids had two explanations:hard work and their parent's encouragement.

1.楼主细细体味一下主从句动作的发生时间,be asked the reason和had two explanations其实几乎是同时发生的,先后意味并不明显.
而且就算是先后发生的,when引导的从句也缺少主语the kids或they,而且从句应该是被动语态,即必须是had been asked,不是吗?
2.此题考查状语从句的省略,即：当状语从句的主语和主句主语相同,且从句的谓语含有be动词时,则从句的主语和be动词可以同时省略.
即：When asked the reason for their success
= When (the kid were) asked the reason for their success
所以答案B为正解.
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