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Most birds find it safe to sleep in the trees, but ________ they have eggs or young chicks, they don’t use a nest.


  1. A.
    why
  2. B.
    how
  3. C.
    unless
  4. D.
    where
C
本题考查连词的用法。unless表“除非”,除非它们下蛋或抚育雏鸟,它们不去使用巢穴。
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【小题2】
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【小题3】
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【小题6】
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