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？
-- by 会员 gmatbiguo (2011/5/7 11:06:00)
看了ls童鞋们的分析觉得选A有道理。
当时做题的时候也是在A和E中徘徊，最后选了A，原因是看到了结论句是说，用这种方法算
最大的海洋年龄。
然后A取非的话是有的时候会有大量的盐，所以说算出来的年龄肯定很大了！（可能超出最大年龄。）
而E取非的话就是说有些盐会消耗掉，那样的话，算出来的年龄肯定就小了，也就不可能是maximum了。所以选了E……>_<
-- by 会员 清水涟漪 (2012/4/9 17:35:16)
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？
-- by 会员 gmatbiguo (2011/5/7 11:06:00)
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）
-- by 会员 Aviva0307 (2011/6/20 20:04:14)
