完全不懂这个cr的突破点 求解答

玛德滞涨

22. GWD27-Q22:
Whales originated in the freshwater lakes and rivers of ancient Asia about sixty million years ago.  Not until about ten million years later did species of whales develop specialized kidneys enabling them to drink salt water.  Although fossil evidence shows that some early whale species that lacked such kidneys sometimes swam in the Earth’s saltwater oceans, these species must have had to return frequently to freshwater rivers to drink.
Which of the following is most strongly supported by the information given?
A.        Fossils of whale species dating from between sixty million and fifty million years ago will not be found on continents that were at the time separated from ancient Asia by wide expanses of ocean.
B.        Among whale fossils that date from later than about fifty million years ago, none are fossils of whale species that drank only fresh water.
C.        Fossils of whale species that drank fresh water will not be found in close proximity to fossils of whale species that drank salt water.
D.        The earliest whales that drank salt water differed from fresh-water-drinking whales only in their possession of specialized kidneys.
E.        Between sixty million and fifty million years ago, the freshwater lakes and rivers in which whales originated were gradually invaded by salt water.
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答案是a
nn能解释一下吗

玛德滞涨

alzn2765 发表于 2016-4-2 13:35
Whales originated in the freshwater lakes and rivers of ancient Asia about sixty million years ago.  ...

对 就是数学的逆否命题

emmahiggins09

alzn2765 发表于 2016-4-2 13:35
Whales originated in the freshwater lakes and rivers of ancient Asia about sixty million years ago.  ...

说的很对。

归纳题在题干中是没有结论的。应该只有 premise. 即使有貌似结论的语句应该也是 intermediaire conclusion 也就是有可以做题干中premise 的结论而又是main conclusion 的 premise

alzn2765

Whales originated in the freshwater lakes and rivers of ancient Asia about sixty million years ago.  Not until about ten million years later did species of whales develop specialized kidneys enabling them to drink salt water.  Although fossil evidence shows that some early whale species that lacked such kidneys sometimes swam in the Earth’s saltwater oceans, these species must have had to return frequently to freshwater rivers to drink.
Which of the following is most strongly supported by the information given?
A.        Fossils of whale species dating from between sixty million and fifty million years ago will not be found on continents that were at the time separated from ancient Asia by wide expanses of ocean.

首先，这题的问题“which of the following is most strongly supported by the information given?”就已经说明了这题是一个归纳推理，所有题干中的任何信息都可能是选项的前提，选项是结论。也就是说你在题干中找逻辑关系是没有用的，因为选项中的结论可能是题干中任意一句的结论。即使你找到了题干中的结论，答案也不一定是针对这一句的归纳。

其次，题干中就没有因果逻辑关系，只有信息。Although fossil evidence shows that some early whale species that lacked such kidneys sometimes swam in the Earth’s saltwater oceans, these species must have had to return frequently to freshwater rivers to drink. 尽管...，但是....。这是一个让步句，没有因果关系在里面。
你说的“果”：早期鲸鱼没有能力离开亚洲大陆 在题干中就没有提及，题干中只说了 这些没有肾的鲸鱼即使可以暂时的游到海里。

再次，“因为鲸鱼没有在其他大陆上被发现，所以证实了鲸鱼没有能力离开亚洲大陆。”这句话的因果关系就说反了：一定是“鲸鱼没有能力离开亚洲大陆”在先，“鲸鱼没有在其他大陆上被发现”（被现在的人发现）在后。哪个是因哪个是果？
所以，这句话的逻辑关系即使真的存在也应该是“因为鲸鱼没有能力离开亚洲大陆，所以鲸鱼没有在其他大陆上被发现”。那么其逆否命题“如果鲸鱼有在其他大陆上被发现，则鲸鱼有能力离开亚洲大陆”为真，剩下的都真假不定。

再次，你依旧在犯我之前的说的错误：
A--->B为真，只能推出 非B--->非A 为真
非A--->非B  真假不定
你说的：
因为鲸鱼没有在其他大陆上被发现，所以证实了鲸鱼没有能力离开亚洲大陆。也就是支持了文中结论---鲸鱼要回亚洲大陆喝淡水。鲸鱼只能活动在亚洲大陆周围

反过来，因为鲸鱼在其他大陆上被发现，所以证实了鲸鱼能离开亚洲大陆，证实了鲸鱼有能力喝海水，也就是反驳了了鲸鱼必须回到亚洲大陆和淡水。这就变成了削弱原文结论。

也就是说
因为鲸鱼没有被在其他地方发现，所以鲸鱼不能喝海水
因为鲸鱼在其他地方被发现了，所以鲸鱼能和海水

其实能不能去别的大陆代表着能不能喝海水。
能喝海水就能去其他大陆；
不能喝海水就去不了其他大陆。

这个错误你犯了3次。。。

alzn2765

elusive 发表于 2016-4-2 09:50
我再找几个题看看

你加我微信算了
我发帖里能找到

alzn2765

elusive 发表于 2016-4-2 09:35
我其实不是说用neg test来做，的意思是这样的：
如果鲸鱼在其他大陆上被发现了，那么结论鲸鱼无法和海水 ...

你如果这么想就是错误的：
如果鲸鱼在其他大陆上被发现了，那么结论鲸鱼无法和海水就不成立。 （鲸鱼在其他大陆上被发现了--->鲸鱼可以喝海水）
反过来如果鲸鱼没有被发现，那么久支持了结论。（如果鲸鱼没有被发现--->鲸鱼可以喝海水）

A--->B为真，则 非A--->非B 真假不定

Assumption的定义是结论成立的必要条件。如果有外国人说assumption是结论成立的充分条件，这个外国人必然说错了。你想想啊，如果assumption就是充分条件，还要前提干什么？直接assumption就让结论必然成立了，前提不是多余的？所有补桥的条件都是必要条件，不可能是充分条件。

你真假言命题的部分和充分必要条件的定义需要再回顾一下。

alzn2765

elusive 发表于 2016-4-1 02:34
我看prep上面的因果题加强和assumption就是取非然后削弱。

只有assumption题可以取非验证，因为assumption是结论成立的必要条件。
当加强是Defender加强的时候，此时跟Assumption有交集。当加强是“补桥”的时候，此时加强等于assumption。只有这两种情况可以用Negation Test验证，因为此时 加强＝assumption
当前提结论之间没有gap的加强时，加强条件可能是结论的既不充分也不必要条件，此时Negation Test无效。