My father walked _____ in the room, looking as if he was thinking over something.A.now and thenB.up and downC.again and againD.over and over
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B解析now and then表示时间；again and again和over and over表示次数。这三个短语都不符合语境。walk up and down in the room意思是“在房间里踱来踱去”。