题目内容
【题目】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
【答案】C
【解析】by the time意为“到……时”，引导的从句谓语用一般过去时时，主句用过去完成时表示已完成的动作。
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题目内容
【题目】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
【答案】C
【解析】by the time意为“到……时”，引导的从句谓语用一般过去时时，主句用过去完成时表示已完成的动作。