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.
请各位大侠指导一下这类题的做法
首先说一下我的思路：must be true means that if it is wrong, then the conclusion is wrong. right?换句话说，没有该选项，就没有答案，所以对每一个选项取非。可是具体应该怎么考虑呢？作者: season5924 时间: 2011-4-7 21:11
选B吧。
原文的推导过程：only by moon -> angle/tilt; no tilt -> no life
所以，no moon->no tilt->no life B正确。
A, C不充分；D,E与原题无关。作者: ozymendias 时间: 2011-4-8 06:35
If Earth’s Moon were to leave Earth’s orbit -----〉That angle cannot be kept fairly stable ---à
a planet’s climate is too extreme and unstable to support life.( based on Without such a stable and moderate axis tilt, a planet’s climate is too extreme and unstable to support life.)
(B) If Earth’s Moon were to leave Earth’s orbit, Earth’s climate would be unable to support life.
