feifei-16请教

kcnooy108

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.

key：B

为什么C不对了？

georgelhb

C太片面，还要考虑其他参照物，因为引力是相互的

kcnooy108

Without such a stable and moderate axis tilt, a planet’s climate is too extreme and unstable to support life.-----〉这个不是就可以推出么。

在做推理题的时候不能多做外推的，不能用常识推的

Dancy123

题目里面说的是没有stable and moderate axis til，一个行星上的气候就无法支持生命。是非A非B得形式

但是C说的是只要有stable and moderate axis til，就可以支持生命。是AB的形式

他们两个是不一样的，所以不选C

[此贴子已经被作者于2009-5-19 21:55:18编辑过]

kcnooy108

   明白了，非A非B是必要条件，A到B是充分~

Thanks。。。