Question

By the time he was twelve, Edison _______ to make a living by himself.

A．would begin

B．has begun

C．had begun

D．began

Answer 1

C

試題分析：考查時(shí)態(tài)。By…到…為止；與完成時(shí)連用。后面接the time he was twelve是過去時(shí)，故主句中使用過去完成時(shí)。句意：到他12歲的時(shí)候，Edison已經(jīng)開始靠自己謀生了。故C正確。
點(diǎn)評：時(shí)態(tài)題中對by的考查是最關(guān)鍵的，by到…時(shí)為止；與完成時(shí)連用。