一个CR问题

祚幼祚幼

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A, 我选E。觉得两个都对。

soulwangh

Negate E.  If some of the salt are used up by biological activity, this consumption will not necessarily influence the conclusion.

Analogy：

A tube pipes water into a pool, at the same time the pool are draining off water at a rate lower than that of the pipe line.

Given the increase in water volume and the time needed, we still can calculate how long will it take to make the pool full of water.

祚幼祚幼

soulwangh 发表于 2013-12-4 13:30
Negate E.  If some of the salt are used up by biological activity, this consumption will not necessa ...

我理解的你的意思 可是测量盐分和测量体积可以等同吗？

soulwangh

祚幼祚幼 发表于 2013-12-4 16:19
我理解的你的意思 可是测量盐分和测量体积可以等同吗？

It is just an analogy.

They are not totally equal to each other. Otherwise, I should repeat the  original question again.

I want to use the water example to make you clear about why we can calculate the time in which salt amass in the ocean(water piped in to the pool), even when biological activities is depleting some amount of salt(water drained from the pool).

祚幼祚幼

soulwangh 发表于 2013-12-4 16:46
It is just an analogy.

They are not totally equal to each other. Otherwise, I should repeat the   ...

明白了！讲得好清楚，谢谢。

soulwangh

祚幼祚幼 发表于 2013-12-5 11:52
明白了！讲得好清楚，谢谢。

Glad to help.