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题目
题型:不详难度:来源:
By the time Einstein was 14 years old, he ________ himself advanced mathematics.
A.has taughtB.taught
C.had taughtD.was teaching

答案
C
解析
by the time 引导时间状语从句,主句中的动作发生在从句中的动作之前。故用过去完成时。
核心考点
试题【By the time Einstein was 14 years old, he ________ himself advanced mathematics.】;主要考察你对一般现在时等知识点的理解。[详细]
举一反三
We have done things we ought not to have done and ________ undone things we ought to have done.
A.leftB.leave
C.will leaveD.leaving

题型:不详难度:| 查看答案
— Why weren"t you at the meeting?
    — I ________ for a long distance call from my sister in America.
A.was waitedB.was waiting
C.has waitedD.have been waiting

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The little boy is dirty from head to foot because he ________ in the mud all morning.
A.has playedB.is playing
C.has been playingD.was playing

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The new dictionaries are very useful. They ________ well and ________ already .
A.sell; have been sold out
B.sold; had sold out
C.sell; sell out
D.are sold; have been sold out

题型:不详难度:| 查看答案
It seems water ______ from this tap for some time. We’ll have to take it apart to put it right.       
A.had leakedB.is leaking
C.leakedD.has been leaking

题型:不详难度:| 查看答案
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