问题
选择题
By the time he was twelve he ______ a chemistry lab of his own.
A．built
B．has built
C．had built
D．was building
答案
答案：C
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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By the time he was twelve he ______ a chemistry lab of his own.
A．built
B．has built
C．had built
D．was building
答案：C
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。