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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.
错选E，等式可以求解建立在盐度的增量是均匀的，如果过去几百年特别大或特别小，这几百年的样本就不具有代表性了。写到这又觉得这道题好像是枚举推理了呢...答案对E的否定有些牵强，官方解释说如果盐被生物消耗的速率也是均匀的，即使存在也无妨，选项又不说是不是均匀，坑人嘛。
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