Helen ( ) her keys in the office so she had to wait until he

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Helen ( ) her keys in the office so she had to wait until her husban ( ) home.
A.has left,comes B.left; had come C.had left; came D.had left; would come
答案是选C把,为什么

根据句中的had,可得知是对【已发生事情】的描写,故宜用过去时态,排除A.
接下来排除B,需分清这两个动作的先后.
排除D的理由是：【主将从现】即条件、时间状语需用一般时代替一般将来时,用一般过去时代替过去将来时.

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