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    本题由chris提供
2712次学习

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.


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答案:
A
地球河流持
续携带溶解的盐入海。因此,依靠海水过去数百年的盐含量增加速度,可计算海水盐度从初始为无盐到现在浓度需要的时间,地球海洋的最大年龄可以估计出来。 假设题 A. 过去数百年河水溶解盐数量不是异常的多;取反即如果溶解盐数量异常多,则盐含量增加速度显然会高估,从而削弱结论,正确 B. 所有地球河都有同样盐含量; 取反盐含量不同,也不影响计算结果,无法削弱,排 C. 盐从海底直接溶解进海洋; 说明河流不是海水盐的唯一来源,削弱,排 D. 没有方法好过盐含量法估计海水年龄;无关,排 E. 没有盐被海洋生物行为耗尽;无关,排

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