By the time he was twelve,Edison（） to make a living by himself A.would begin B.has begun C.had b

题目

By the time he was twelve,Edison（） to make a living by himself A.would begin B.has begun C.had b

答案

答案是C,had begun
By the time he was twelve,Edison had begun to make a living by himself.
By the time表明截至到某一段时间为止,后面的句子须用完成时态对应.