题目内容
Someone knocked at the door he was doing his homework.
A.after | B.when | C.until | D.as soon as |
B
试题分析:句意:有人敲门,他正在做作业。After在……之后;when当……的时候; until直到; as soon as一……就。结合前后句子意思可知该选B。

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