. By the year 2020 scientists _____ a lot of research on AIDS.A．had doneB．doC．ar

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. By the year 2020 scientists _____ a lot of research on AIDS.

A．had done

B．do

C．are doing

D．will have done

答案

解析

略

举一反三

But for the fact that the firefighters _____ at the spot in time, more people ______ their lives in the fire.

A．arrived; died	B．had arrived; would lose
C．arrived; would have lost	D．has arrived; could have lost

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I ________ to help you with your homework, but I couldn’t spare any time. I ________ a composition last night and I’ll finish it today.

A．wanted; wrote	B．had wanted; was writing
C．have wanted; wrote	D．wanted; have been writing

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Flight 3010______,I must be off now or I’ll be late.

A．to announce

B．is announced

C．is being announced

D．announced

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By the time you ____ in, I ____ two letters.

A．had come, had written	B．came, wrote
C．come, have written	D．came, had written

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—I’ll call you at 9 tomorrow morning, OK?
—You’d better not, I ______ the piano then.
A. will be practicing B. am about to practice

am practicing D. practiced

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