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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.
着题目也太难了吧（一定要注意体会名词的修饰部分！）
P1：河流携带溶解的盐流进大海
C：通过测量过去近百年的海洋盐度增长就可以得出the maximum age of the Earth's oceans（一定一定要注意这个'最大年龄'的限制）
注意：最开始看这个题的时候把gap想错了...想了两个看似有理的gap：①是不是只有river是海洋salt的唯一来源②river里的salt是不是经常变来变去的...其实真的是没有抓住重点也没有仔细去审题==》题目在得出结论的时候就已经和river 没啥事儿了，相当于第一个gap就不存在的
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