[求助]GWD逻辑一道，求助！

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.

参考答案是A。但是我觉得C好像也挺好的，请高手指点。谢谢

A排除了中间盐减少干扰结果的情况。

C 有大洋底部过滤到海洋里的盐，使中间盐的量增加了，评估结果就不准确了

E为什么不对，好像也跟A的作用差不多

我们群里人是这么解释的。。

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
管你盐是怎么来的，我只计算海水里的盐增加量就足够了（就是已经包括河水加盐减去生物耗盐的可能，所以E错）。但如果过去几百年河水盐unusually多了，海盐增加量当然比以前unusually高，把这个几百年里unusually高的增加量不恰当的推广到整个历史时期里，算出来的时间当然比真实时间的短。