It never occurred to humans until the mid-1990s _____ some animals can be cloned.

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• 1— Haven't seen Lucy recently, what's happened? 一 Oh, it's more than two months _____ she worked here.

  A.which

  B.that

  C.before

  D.since

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• 2_____ I accept that he is not perfect, I do actually like the person.

  A.While

  B.Since

  C.Before

  D.Unless

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• 3You'd better take an umbrella _____ it rains.

  A.in case

  B.unless

  C.as long as

  D.ever since

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• 4The little boy won't go to sleep _____ his mother tells him a story.

  A.or

  B.unless

  C.but

  D.whether

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• 5John couldn't finish his words _____ something had struck his throat.

  A.though

  B.as though

  C.when

  D.since

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• 6As it reported, it is 100 years _____ Qinghua University was founded.

  A.when

  B.before

  C.after

  D.since

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• 7The school rules state that no child shall be allowed out of the school during the day, _____ accompanied by an adult.

  A.once

  B.when

  C.if

  D.unless

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• 8— How long do you think it will be _____ China sends a manned spaceship to the moon? — Perhaps two or three years.

  A.when

  B.until

  C.that

  D.before

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• 9Last month I came to Britain. My English has improved a lot _____ I use it all the time.

  A.since

  B.while

  C.when

  D.as

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• 10____ most of the earth's surface is covered by water, fresh water is very rare and precious.

  A.As

  B.Once

  C.If

  D.Although

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