OG12 117

Suri在奋斗

in order to weaken an argument you have to find the premise for that argument - here the author uses the facts about spiral galaxies - the fact that their spin does not change as you get further from the center (where there is less luminous mass) and therefore there must be dark mass that takes up the difference. Then in the next paragraph he uses this information to support the fact that over 90% of the dark matter is not detected.

This type of reasoning is akin to saying that becuase we have found that black widow spiders are extremely poisonous then most of the spiders are also extremely poisonous - this isn't true unless most of the spiders in the world are Black widows. similarly the above argument rests on the fact that spiral galaxies make up enough of the univers to make a blanket stament. This is why A weakens it - becuase if Spiral galaxies less common than other galaxies that don't have the same properties then you can't make that conclusion

curtis0063

今天也在练习这篇文章，其中第二段是关键，我看了好几次才看懂，116和117题主体信息都在第二段，再加上前后段一点信息来判断，都是很难的题目。

关于本题，主要是要考 oversimplification，也就是说 Spiral galaxies 只是其中一种，各位有空可以到 Wiki 看这篇，可以的话，再到 Youtube 查 velocity of spiral galaxy，会比较有概念。

http://en.wikipedia.org/wiki/Galaxy#Types_and_morphology

http://youtu.be/9B9i4vjj5D4

所有选项，除了 A 以外，其他其实都比较无关，尤其是 E ，个人认为文中已指出旋转速度，核心和外围是相近，所以可以砍了。