GWD 12-Q29

ken_miu

GWD-12-Q29:！！

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.

The answer is A, but why B is incorrect?    If the salt level of river keeps the same, it will not affect the salt level of the ocean.

ken_miu

顶啊顶。。 有没人 帮忙解答啊？。。。谢谢啦

pdsb

假设一定要是题目结论的必要条件。我想B不是必要条件

随便据个例子，假如东半球的河是一个盐度，西半球的是另一个盐度，那按照这个方法也可以计算出来海洋的年龄。

B说“在任何时间，全世界河流的盐度都是一样”。问题就是说得太严格了，不是题目成立的必要条件。

[此贴子已经被作者于2009-4-5 9:29:11编辑过]