23. Tom had to be told two or three times he could remember what the teacher said.A. befo

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(答案→)A. before
B. when
C. until
D. As
解析：
23．A(解析：考查连词。before 到……为止；在……之前when“当……时候until直到……为止”as“当……时候”，until强调动作的延续性，其中tell并非延续性动词，另根据句意“老师说两三遍之后汤姆才能记住。”因此选A。)