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What do scientists say about the collision of an asteroid with Earth?
A) It is very unlikely but the danger exists.

B) Such a collision might occur once every 25 years.
C) Collisions of smaller asteroids with Earth occur more often than expected.
D) It‘s still too early to say whether such a collision might occur.

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出自：河南师范大学-小学教育（本科)-大学英语Ⅱ

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