By the time he was twelve he a chemistry lab of his own.A. builtB. has builtC. had builtD

发布时间：2020-08-15 00:13:53

 By the time he was twelve he      a chemistry lab of his own.
A. built
B. has built
C. had built
D. was building

网友回答

A. built
B. has built
(答案→)C. had built
D. was building
解析：有by the time 引导的短语或从句，主句应该是完成时态，至于是什么完成时态，就看by短语或从句中的时态了。
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