纠结与A和E之中，GWD-12-Q29，求解释！

veralove3271

The Earth’s rivers constantly carry dissolved salts into its oceans.  Clearly, therefore, by taking the resulting increase in salt levels in the oceans over the past hundred years and then determining how many centuries of such increases it would have taken the oceans to reach current salt levels from a hypothetical initial salt-free state, the maximum age of the Earth’s oceans can be accurately estimated.

Which of the following is an assumption on which the argument depends?

A.    The quantities of dissolved salts deposited by rivers in the Earth’s oceans have not been unusually large during the past hundred years.
B.    At any given time, all the Earth’s rivers have about the same salt levels.
C.    There are salts that leach into the Earth’s oceans directly from the ocean floor.
D.    There is no method superior to that based on salt levels for estimating the maximum age of the Earth’s oceans.
E.    None of the salts carried into the Earth’s oceans by rivers are used up by biological activity in the oceans.

答案选了A，但我我有看到解释说选E.我自己也选了E，但觉得A也蛮有道理的。请NN们帮忙分析一下，到底哪个对的？

shlshingse

I try A: The quantities of dissolved salts deposited by rivers in the Earth’s oceans have not been unusually large during the past hundred years.May have been unusually small.

LoveY

我认为选A。
A说过去一百年的盐量不能unusually large——必须保证each century和the past hundred years盐量一样，才能用累积总量÷过去一百年的盐量，得出时间。

E说的海洋生物有没有消耗盐，其实并不重要。只要每个世纪海洋生物消耗的盐都一样多就行（每个世纪，海洋中净增盐量恒定即可）

hebby0513

A 一点悬念都没有。

你仔细想想，E是被A包含了。 A项大气。

我去年9月考的，就有这个题。

SiyangWu

这道题是挺难的，我第一次也是纠结于A和E，但后来想了后明白了到底怎么回事。。。先说B，大家质疑的最多的，At any given time, all the Earth’s rivers have about the same salt levels.这里的rivers是指同一个given time的，所以要求rivers都有一样的盐浓度是没有必要的，你们想的应该是不同时期的rivers盐浓度相同，这个有关，也有影响，但不是GMAC的人的想法。。。再说E，其实这个也很有迷惑性，但是其实used up一看我就觉得有问题，其实每个时期进入量by rivers和消耗量by biological activities的差值才是salt level的increase，有后面这个也是不影响各个时期的increase的，只要各个时期这个量近似相等，当然本题没有探讨这个问题，E只是提到了消耗量，但并不会因为没有这个assumption就没有了对应的conclusion。不知道我讲明白没有，大家可以借鉴下。。供以后大家参考。。