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标题: GWD-12-29有不同意见，请NN检查我的问题在哪里 [打印本页]

作者: 清蒸鲈鱼 时间: 2005-12-21 22:11
标题: GWD-12-29有不同意见，请NN检查我的问题在哪里

Q29:

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.

很多NN都选A.

理由是，对A取非后，The quantities of dissolved salts deposited by rivers in the Earth’s oceans have ~~not~~ been unusually large during the past hundred years. 这样计算出来的Age大过实际的。但是，题目中不就是要算maximum age 吗？从数学的角度来看，所谓maximum ，就是最大的可能性。也就是说取非以后结论反而是加强了。那么反之，A本身就削弱了题目。

而E，说没有盐分被消耗掉，也就是把含盐量的可能性放到了最大，这样得出来的结果不正好就是maximum age 吗？

因为实在想不通之前大家的说法，所以开出一个新贴（怕跟在老贴后没人理我:p），希望有人指点一下。谢谢了！

作者: yangxiaogang 时间: 2005-12-21 23:57
楼主想反了，如果前几年大量盐分流入大海，那算出来的最大理论值可能小于实际的最大值。所以A是假设，加强了结论。E刚好相反。

作者: zenger 时间: 2005-12-22 02:34

题目是根据盐含量的变化推算时间长久。

A指出了盐含量的每年变化可能是不平均的，因此不准

E说盐含量的影响因素中可能有负因子。

作者: 2000000006 时间: 2005-12-22 08:51

就是E表明了这个负因子造成盐的消耗使得测量可能不准，那么对这个情况的排除才可能是assumption啊，这道题我第一眼就选E,有问题么？thanks.

作者: yangxiaogang 时间: 2005-12-22 09:41

E 是错误的，刚好相反

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