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16. The axis of Earth’s daily rotation is tilted with respect to the plane of its orbit at an angle of roughly 23 degrees. That angle can be kept fairly stable only by the gravitational influence of Earth’s large, nearby Moon. Without such a stable and moderate axis tilt, a planet’s climate is too extreme and unstable to support life. Mars, for example, has only very small moons, tilts at wildly fluctuating angles, and cannot support life.
If the statements above are true, which one of the following must also be true on the basis of them?
A. If Mars had a sufficiently large nearby moon, Mars would be able to support life.
B. If Earth’s Moon were to leave Earth’s orbit, Earth’s climate would be unable to support life.
C. Any planet with a stable, moderate axis tilt can support life.
D. Gravitational influences other than moons have little or no effect on the magnitude of the tilt angle of either Earth’s or Mars’s axis.
E. No planet that has more than one moon can support life.
我承认B对，但不知道A为什么不对？？谢谢！
A only by B。 A,B到底互为什么条件？是B->A吗？ | 
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发表于 2005-4-30 07:54:00
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