_____ they were sweeping the floor ,John came backA thoughB whileC untilD before
问题描述：
_____ they were sweeping the floor ,John came back
A though
B while
C until
D before
答
B,过去进行时
答
B 进行时态用词，在。。。那会儿。
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答
选B,while表示“当……时”,特别地用于表示“当……正在做某事时”
答
B