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题库 / Prep2012-CR-73
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?
The quantities of dissolved salts deposited by rivers in the Earth's oceans have not been unusually large during the past hundred years.
At any given time, all the Earth's rivers have about the same salt levels.
There are salts that leach into the Earth's oceans directly from the ocean floor.
There is no method superior to that based on salt levels for estimating the maximum age of the Earth's oceans.
None of the salts carried into the Earth's oceans by rivers are used up by biological activity in the oceans.
这题属于super hard高分题了吧，并不是楼下说的因果推理。
听了Ron大神的解说，仔细想想就一个很简单的原理：每年的增量*年数=最后的总增量
所以年数=总增量/年增量，已知最后的总增量相同，要保证年数正确，就要使年增量相同，也就是年增量每年都一样，也就是A。
E即使盐被一些生物消耗，但只要保证年增量一样，最后的年数也是一样的。
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