题目内容
By the time he was twelve, Edison __________ to make a living by himself.
A. would begin B. has begun
C. had begun D. was begun
C
【解析】
试题分析:考查时态。By…到…为止;与完成时连用。后面接the time he was twelve是过去时,故主句中使用过去完成时。句意:到他12岁的时候,Edison已经开始靠自己谋生了。故C正确。
考点:考查时态
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