They repeated the experiment several times ______ they were sure that the result was reliable.

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问题 They repeated the experiment several times ______ they were sure that the result was reliable.

选项 A、until
B、for
C、since
D、when

答案A

解析 until引导时间状语从句，表示动作持续到某一时间点。其他选项不合题意。例如：He waited for his friend at the bus stop until the last bus came．(他在车站等他的朋友，一直等到最后一班车来。)

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大学英语三级B级

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