gwd-12-29

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?

1. The quantities of dissolved salts deposited by rivers in the Earth’s oceans have not been unusually large during the past hundred years.


2. At any given time, all the Earth’s rivers have about the same salt levels.


3. There are salts that leach into the Earth’s oceans directly from the ocean floor.


4. There is no method superior to that based on salt levels for estimating the maximum age of the Earth’s oceans.


5. None of the salts carried into the Earth’s oceans by rivers are used up by biological activity in the oceans.

我怎么看A，B，E都像啊？

b is wrong coz even all the rivers have different salt levels ,the amount of salts taken by the oceans at a given time might be constant.

e is wrong coz the consuming of salt has already been taken into consideration

a is the right answer

多谢berry兄。berry兄的逻辑真强！佩服啊!

老兄玩笑了，呵呵，我们都是在诸多大牛的阳光下努力成长的，只不过是偏巧这道题我明白而已。

   我说一下我的理解，但不确定，有点搞。请斑竹看是不是这样理解的，确认一下

   过去100年中盐增加总量 /  100年 =  每年恒定的进入海的盐量

   现在总的海中的盐量（默认初始为0） /  每年恒定的进入海的盐量（上面求得）=  海形成的最大年龄（暗示可能盐有消耗，因此是最大年龄）

   A说：过去100年中进入海中的盐量不能异常的高（暗示如果异常高的话，每年恒定的进入海的盐量这个数值就不能作为第二个等式的分母）所以是assumption

   B说：在一个特定的时间，所有的河里盐量一致——》无关，不能从原文信息中衍生

   E说：海中的盐没有被生物活动所消耗——》文章说了求的是最大年龄，因此有消耗也属于范围之内

   我一开始选了E，好象还是句子理解有问题。应该是A

我觉得是E.

如果这段期间内,海盐有被消耗掉的话,实际现在得到的海盐量就少了.计算出来的年份也会偏小.怎么反而可以成为the maximium age 呢?

有人能指点指点我吗? 谢谢。

VOTE FOR  E

D。对D取非，有些年的盐异常高，则目前的盐度被高估，比如计算出是10M年，实际为8M年。海洋最大年龄为10M年没错。不能否定结论。

E。对E取非，有些盐被消耗，则目前的盐度被低估，比如计算值为10M，实际为12M，海洋最大年龄为10M是错的。否定结论。故为答案。