GRE93年2月section3短阅读,

GRE93年2月section3短阅读,
It is now established that the Milky Way is far more extended and of much greater mass than was hitherto thought.However,all that is visible of the constituents of the Milky Way’s corona (outer edge),where much of the galaxy’s mass must be located,is a tiny fraction of the corona’s mass.Thus,most of the Milky Way’s outlying matter must be dark.
　　Why?Three facts are salient.First,dwarf galaxies and globular clusters,into which most of the stars of the Milky Way’s corona are probably bound,consist mainly of old stars.Second,old stars are not highly luminous.Third,no one has detected in the corona the clouds of gaseous matter such as hydrogen and carbon monoxide that are characteristic of the bright parts of a galaxy.At present,therefore,the best explanation—though still quite tentative—for the darkness of the corona is that the corona is composed mainly of old,burned-out stars.
　　19.It can be inferred from the passage that,compared with what they now think,until fairly recently astronomers believed that the Milky Way
　　(A) was much darker
　　(B) was much smaller
　　(C) was moving much more slowly
　　(D) had a much larger corona
　　(E) had much less gaseous matter
　　20.The passage presents which of the following as incontrovertible?
　　I.The low luminosity of old stars
　　II.The absence of clouds of gaseous matter from the corona of the Milky Way
　　III.The predominance of globular clusters and dwarf galaxies in the corona of the Milky Way
　　(A) I only
　　(B) III only
　　(C) I and II only
　　(D) II and III only
　　(E) I,II,and III

呵呵,答案为19. B 20. A .
楼主给分这么高,不好意思不出力,说一下答案得出方法：
19. 来自“It is now established that the Milky Way is far more extended .than was hitherto though”,意为：现已证明银河系比以往认为的更大.
20. 题干问下面哪一项在文中被看做“不可辨驳的”. I. 来自“Second, old stars are not highly luminous. ”； II. 来自“Third, no one has detected in the corona the clouds of gaseous matter”；III.来自“ First, dwarf galaxies and globular clusters, into which most of the stars of the Milky Way’s corona are probably bound”.其中, I.是陈述事实；II 中有no one 说明只是人们没有发现,不能证明不存在.III中有probably.因此,只有I是作为“不可辨驳的”事实的.
再问： 能解释一下这句话嘛吗？ It can be inferred from the passage that, compared with what they now think, until fairly recently astronomers believed that the Milky Way。。。
再答： 从文中可以推论出：与他们现在所持的观点相比，直到最近天文学家们都一度认为银河系______。
再问： 那为什么答案是much smaller?
再答： 从“It is now established that the Milky Way is far more extended ......than was hitherto thought” （现已证明银河系比以往认为的更大）中可以看出，科学家对银河系的大小的判断有了变化，现在认为银河系比以往认为的更大，也就可以推出过去一度认为 "更小"。你可能没有注意前文“与他们现在所持的观点相比”这句话。