gwd-12-29

liyuan

关键是确定一个上界．

对Ａ取非，算出来的结果偏大没有关系

对Ｅ取非，如果盐有消耗的化，那么算的结果就偏小了，对估计最大值是有影响的．

robertchu

A is the best answer.  This is an assumption question, so one can try deny test.

Deny E, we get “Some of the salts ... are used up by biological activity in the oceans.”  How will this affect the original argument?  Since “some” can be either “a significant portion” or “a insignificant portion”, the original argument may or may not fall apart.  It’s is not conclusive, therefore, E is not a good answer.

Now try to deny A, we get “The quantities of dissolved salts deposited by rivers ... have been unusually large during the past hundred years.”  If so, then obviously one crucial factor used in the calculation, is thrown into question, and consequently, the original conclusion “the maximum age of the Earth’s oceans can be accurately estimated” is severely weakened.  Therefore, we can conclude A is a necessary assumption and the best answer.

bloodcherry

vote A definitely

lawyer_1

这道题已作过2个多月了，现在再回来想一想，其实理解了该题的主要词的含义和严格遵循所有推理信息来之原文，就明白为何E是正确答案，A不是。

1。必要型假设题有两类：DEFENDER（排除其他可能性，排除削弱或攻击结论成立的可能性因素）和SUPPORTER（GAP），显然该题属于DEFENER类

1。resulting increase 。由于河流的SALT流入海洋导致的盐分的增加，用这增加去计算海洋的年龄，实际就是指海洋盐分增加的速率，即每个单位年度的盐分增加量，这个单位年度可以是100年，也可以使50年，原文没说，我们不知道，反正是个速率。这个速率的最大特点是原文没告诉怎末计算出来，任何关于他如何计算出来的说法都是典型的加入自己的想象，这个最大特点是我们很难攻击它，因为不知如何算出速率，不知用那一年的数据，不知如何加权以消除偏差。等等。反正这是个最难攻击的词。只有一个原因，原文没给其它任何信息。

2。原文计算海洋最大年数的方法：current salt levels （即现在海洋的盐的浓度或水平）除以resulting increase 。因为起点是salt-free state，即零。所以，该题可攻击的因素只剩下current salt levels （即现在海洋的盐的浓度或水平），即current salt levels 是否能反映真实的现在应该有的浓度，即在该速率下，花多少年所能达到的浓度。如果如E取非所说，即有些河流流入的盐没了，则目前的salt levels 低估了，算出的年度偏小，结论不能成立。

3。A选项攻击的是速率，但是，它只能可能性的攻击它，就是说，如果用的数据恰好是不正常的数据，则能影响它，但也有可能取的数据正好。其实产生这些情况的原因在于原文没给任何有关计算速率的信息。所以它不能使结论不能成立，只能使结论可能不成立。所以不是答案。

horsefish

我选A

E选项是文章中已经考虑过的了, 不需要再考虑了

roggy2002

应该选E。

由原文可知计算海洋最大年龄的关键是必须知道the resulting increase in salt levels in the oceans over the past hundred years, 而A告诉我们这个数字变大了，那结果无非就是我们的估计值变大了，但这也是正确的值。而把E取非，告诉我们本来应该计入的数值被损耗掉了，那么我们的估计值就不可能准确了，所以应选E

exan

我觉得是A

A取非：“最近几百年的含盐量异常高”，

假设正常情形，每年盐量为a；虽然最近几百年的含盐量异常高，但是有可能很久以前含盐量比较低，则平均后每年盐量仍为a。同时，虽然每年的盐量有波动，不影响总量。所以可以得到maximum age，不能weaken结论。

E取非：“有一些盐被生物体消耗”，

盐的总量减少，显然计算得到的age一定是小于实际的age，那么计算得到的age一定不是maximum，weaken结论。

bose0008

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?

1. The quantities of dissolved salts deposited by rivers in the Earth’s oceans have not been unusually large during the past hundred years.
   



2. At any given time, all the Earth’s rivers have about the same salt levels.
   



3. There are salts that leach into the Earth’s oceans directly from the ocean floor.
   



4. There is no method superior to that based on salt levels for estimating the maximum age of the Earth’s oceans.
   



5. None of the salts carried into the Earth’s oceans by rivers are used up by biological activity in the oceans.

A: if it is unusually large, the whole methodology proposed sounds very illogical to derive an accurate estimation.

Negation works for A.

E: Irrelevant:  biological activity is already considered in the process of "taking the resulting in crease in the salt level".

    resulting level=salt level from rivers - salt consumed by biological activity & other activities

[此贴子已经被作者于2004-10-27 1:41:44编辑过]

cranberry

e和a都可以算作是排除他因的选项，我们来看到底哪一个是这个题目要排除的他因呢？先说e吧。我们假定海洋生物消耗掉了部分的盐分，那么只要这个盐分的消耗比率是可知的，而且是稳定的，那么它对海水盐分增加的速率就是一定的，根据几百年的当然可以推导出几亿年的。

而a则不同，如果几百年的速率是过大的，那么按此推算，则结论必然偏小。而且从文章的内容，核心必然在这几百年的问题，而不会是e的泛泛而论。

cappuccino

把A取非，得到The quantities of dissolved salts deposited by rivers in the Earth’s oceans have been unusually large during the past hundred years. 但是，如果知道了过去几百年河里的盐分，即使非常的大，一样可以估算出the maximum age of the Earth’s oceans can be accurately estimated。

所以 (E) IS RIGHT.