再问LSAT Section 8 - 19

oldreaper

Oxygen.18 is a heavier-than-normal isotope of oxygen. In a rain cloud, water molecules containing oxygen-18 are rarer than water molecules containing normal oxygen. But in rainfall, a higher proportion of all water molecules containing oxygen-18 than of all water molecules containing ordinary oxygen descends to earth. Consequently, scientists were surprised when measurements along the entire route of rain clouds' passage from above the Atlantic Ocean, the site of their original formation, across the Amazon forests, where it rains almost daily, showed that the oxygen-18 content of each of the clouds remained fairly constant.

19. Which one of the following statements, if true, best helps to resolve the conflict between scientists' expectations, based on the known behavior of oxygen-18, and the result of their measurements of the rain clouds' oxygen-IS content?
(A) Rain clouds above tropical forests are poorer in oxygen-18 than rain clouds above unforested regions.
(B) Like the oceans, tropical rain forests can create or replenish rain clouds in the atmosphere above them.
(C) The amount of rainfall over the Amazon rain forests is exactly the same as the amount of rain originally collected in the clouds formed above the Atlantic Ocean.
(D) The amount of rain recycled back into the atmosphere from the leaves of forest vegetation is exactly the same as the amount of ram in river runoffs that is not recycled into the atmosphere.
(E) Oxygen-18 is not a good indicator of the effect of tropical rain forests on the atmosphere above them.

以前的回贴http://forum.chasedream.com/dispbbs.asp?boardID=24&replyID=20636&ID=3700&skin=1
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Oxygen.18 is a heavier-than-normal isotope of oxygen. In a rain cloud, water molecules containing oxygen-18 are rarer than water molecules containing normal oxygen.
O18 (含Oxygen.18的水分子) 的比例很低，与O (含普通Oxygen.的水分子)， 句题多多少不知道设为X

But in rainfall, a higher proportion of all water molecules containing oxygen-18 than of all water molecules containing ordinary oxygen descends to earth.
降雨时，

所有O18 降下的比例 （proportion of all water molecules containing oxygen-18）

高于  

所有 O 降下的比例 （proportion of  all water molecules containing ordinary oxygen）

换句话说，所有水分子中， 分为两组O18 和 O， 下雨时O18组 下去的比例要高于 O组下去的比例，例如 在所有O18 有50%下去了， 在所有中O 只有20%下去了

所以 如果下雨 O18在rain cloud中的比例 因该比以前 X 更低， 所以引出下面的科学家的困惑

Consequently, scientists were surprised when measurements along the entire route of rain clouds' passage from above the Atlantic Ocean, the site of their original formation, across the Amazon forests, where it rains almost daily, showed that the oxygen-18 content of each of the clouds remained fairly constant.

所有的云中的O18的比例不变？？ 所以一种可能是在移动的过程中没下雨，这正好是C, 答案确是B

(B) Like the oceans, tropical rain forests can create or replenish rain clouds in the atmosphere above them.

(C) The amount of rainfall over the Amazon rain forests is exactly the same as the amount of rain originally collected in the clouds formed above the Atlantic Ocean.

B 只能所提供了可能性，而且这种可能还需要在补从的雨云中， O18的比例要高于 the clouds formed above the Atlantic Ocean.

我认为B提供了一种不肯定的解释，不应该正确

vrylwj

标准答案是什么呢？

B描述了一个动态系统。
C有点绝对的。好象一次性的感觉，originally 指什么？

oldreaper

以下是引用vrylwj在2003-9-12 3:24:00的发言：
标准答案是什么呢？

B描述了一个动态系统。
C有点绝对的。好象一次性的感觉，originally 指什么？

答案是B

oldreaper

我能明白
c: 从严格意义上讲是不太正确的，因为只从量上来说，也不能推出 ： 所有的云中的O18的比例不变？？ 所以一种可能是在移动的过程中没下雨。因为沿途，火灾目的地都可能增加新的雨云

但是B是正确的话， 就证明一点，解释型的题 "只要提供可能性" 就算对，不一定非要保证结论成立。 如果是这样的话， B就应该是正确的。 相反就应该考虑一下？

大侠！给点意见吧！

youyou3941

我认为是这样的：

在云里，氧18少于正常的氧；下雨时氧18descent to earth比正常氧多

从ocean到Amazon（下雨多）本来clouds里的氧18应该更少（因为都descent to earth了），但现在constant

就是一个数学题了，有了更多的clouds，所以就算氧18单位少了，总数不减