请教OG-9,没有讨论过吗?难道大家都觉得很简单

?Passage 9

51：http://forum.chasedream.com/dispbbs.asp?BoardID=25&ID=79606，供参考。

49

D is the best answer.

In the first paragraph, the author describes Milankovitch”s theory and explains why the theory previously had been considered untestable.

In the second and third paragraphs, the author describes a scientific break-through that has made it possible to test and provide support for Milankovitch’s theory.

Although the author also mentions other factors that potentially could have affected the Earth’s climate, the passage as a whole is concerned primarily with Milankovitch’s theory and the scientific method that has been used to test that theory.

A, C and E do not accurately reflect the content of the passage.

Although the passage does describe a new research method，it supports rather than casts doubt on Milankovitch’s theory.

50.

D is the best answer.

In lines 9-16, the author states that a recent discovery has made it possible to establish a precise chronology of the Earth’s ice ages.

Scientists have used this discovery to test the basic premise of Milankovitch’s theory—that the ice ages were caused by variations in the Earth’s orbit around the Sun.

The author notes in lines 53-56 that the data have established a “strong connection” between orbital variation and ice ages, which confirms the plausibility of Milankovitch’s theory.

However, one can infer from the last paragraph that the author believes factors other than variations in the Earth’s orbit could provide plausible explanations for global climate change.

51

B is the best answer.

The author states that one advantage of obtaining an isotopic record from ocean sediment is that the ocean’s isotopic record is “a more continuous record than that taken from rocks on land”(lines 43-45).

Because a continuous record can indicate more precisely when shifts in the Earth’s climate have occurred, the ocean’s isotopic record would be less useful if it had more gaps in it than the record taken from rocks.

A describes a circumstance that is in fact true, since oxygen 16 is the lighter isotope and, according to the passage, “Almost all the oxygen in water is oxygen 16”(line 17).

This fact clearly has not compromised the usefulness of the ocean’s isotopic record as an indicator of climatic shifts.

Likewise, E would not diminish its usefulness, since isotopic records showing “fluctuations in global ice volume over the past several hundred thousands years” have been sufficient to determine a meaningful pattern (lines 49-53).

If C were shown to be true, Milankovitch’s theory would be weakened, but this would not diminish the value of the isotopic record.

If D were true, researchers would need to accommodate the inconsistency described in evaluating the isotopic record, but, again, this would not compromise the usefulness of the record itself.

52.

C is the best answer.

Lines 13-16 state that the relative volume of land ice can be deduced from the ratio of oxygen 18 to oxygen 16 in ocean sediments.

A, D and E are incorrect because there is no information in the passage to support these statements.

B is incorrect because it contradicts lines 43-45, in which the author states that ocean sediment provides “a more continuous record than that taken from rocks on land.”

简言之，(A) They indicate that sediments found during an ice age contain more calcium carbonate than sediments formed at other times. 文中所述论题和二氧化碳的含量多少无关啊。而(C) They can be used to deduce the relative volume of land ice that was present when the sediment was laid down. 这是新方法有效的关键一环。

53.

B is the best answer.

Lines 23-27 state that when water evaporates from the ocean surface, oxygen 18, a heavier isotope than oxygen 16, tends to be left behind in the remaining ocean water.

Thus, one can infer that evaporated ocean water would contain less oxygen 18 than would the remaining ocean water.

A is incorrect because it contracts information stated in lines 19-27.

C is incorrect because the passage suggests that the water evaporated from the ocean contributes to the growth of continental ice sheets, which should therefore have an isotopic composition similar to that of the precipitation formed from evaporated ocean water.

D and E describe information that cannot be inferred from the passage.

54.

E is the best answer.

Lines 29-33 of the passage state that the calcium carbonate shells of marine organisms are constructed with “oxygen atoms drawn from the surrounding ocean.”

This water contains varying proportions of oxygen 16 and oxygen 18 and, according to the passage, “becomes progressively enriched in oxygen 18”with the onset of an ice age (lines 19-27).

The author states that “The degree of enrichment can be determined by analyzing ocean sediments…composed of calcium carbonate shells of marine organisms (lines 27-31)”.

Thus, it can be inferred that the shells of marine organisms would reflect the isotopic composition of the surrounding ocean water at the time when the shells were formed.

以上简单提示一下，还请楼主再一句句地对照解释看一看。

文章的结构：

提出一种理论：Milankovitch proposed in the early twentieth century

that the ice ages were caused by variations in the Earth’s

orbit around the Sun。紧接着说由于这种理论是很多时候是untesteble,所以介绍一种新的方法来进行test,第二段接下来就说这种具体的方法的原理。第三段论述这种方法的advantage.最后平衡了一下其他的方法，即还有些其他的方法不能因为没被发现而忽略。  

49 b:introducing a new research method that calls an accepted theory into question.

介绍一种新方法来质疑老的理论。这里这个新方法是来test这个理论的。所以不对。

50

51(A) It indicated that lighter isotopes of oxygen predominated at certain times.

(B) It had far more gaps in its sequence than the record taken from rocks on land.我明白mm的困惑，b肯定是对的，因为后面作者提到同位素的优点中提到了他比岩石中的记录要更具连续性，如果缺少这种连续性，肯定会less useful.回到a来，因为16：18比重越大，形成时冰层也越大，所以如果一个记录是以16为主，价值会更小，我觉得也很有道理，看wangyu nn 或哪位高人能指点一下。

52

(A) They indicate that sediments found during an ice age contain more calcium carbonate than sediments formed at other times.

不是含有更多的碳酸盖，而是碳酸该中的氧原子中18和16的比重会不一样，即18要多。

53

c: less oxygen 18 than has the ice contained in continental ice sheets

mm可能理解错了，这里比较o原子是比较海里的，不是和陆地上的冰里的，是因为陆地结冰而降温，造成海里蒸发的水回到海洋的要少，这样蒸发掉的o16回到海洋的就少了，而留下o18就多了。根据这个来确定当时的时间。When an ice age begins, the conti-

nental ice sheets grow, steadily reducing the amount of

water evaporated from the ocean that will eventually

return to it.这句话的理解是关键。

54这个mm看了上面的应该知道了。：（

对于这一问题，我们不妨先看看题目的意思。题目可以算作一道对比取非题，或者一道推断题，或者一道逻辑题。看看解释：B is the best answer. The author states that one advantage of obtaining an isotopic record from ocean sediment is that the ocean’s isotopic record is “a more continuous record than that taken from rocks on land”(lines 43-45). Because a continuous record can indicate more precisely when shifts in the Earth’s climate have occurred, the ocean’s isotopic record would be less useful if it had more gaps in it than the record taken from rocks. 从这里我们可以看出，此题考察的是对比取非的方面，正如解释所说，如果海底取样较陆地上的取样存在更多的中断，那么海底取样的可用性就差了。从此选项，可以先把此题归为对比取非题型，即否定了文中提及的优点，其结果的有效性就降低了。

而我认为，这更是一道逻辑削弱题。因为其它几个选项的排除需要进行逻辑削弱的思考。A describes a circumstance that is in fact true, since oxygen 16 is the lighter isotope and, according to the passage, “Almost all the oxygen in water is oxygen 16”(line 17). This fact clearly has not compromised the usefulness of the ocean’s isotopic record as an indicator of climatic shifts.这里也就是说，选项中的“氧16在某些时候占主要成分”这一点是基本事实。为什么呢？因为文中说“水中大部分是氧16”，这样，至少在非冰河期，氧16占主要成分。因此这是一个基本事实。同时，虽然占主要成分，氧16和氧18的比例也会随着冰河的变化而改变，海底沉积物中的同位素比例也会发应冰河的情况。[其实，既然是基本事实，对海底取样的有效性与否就不构成作用。这在逻辑中的思维就是，对于一个命题来说，重复强调该命题的事实和论据，不能构成对该命题进行削弱的依据。换句话说，就是无关。]

[此方扩号中为多余考虑，一般不用考虑了，不过也可以想想，可以更好地明白氧16和氧18的比例变化过程，但和做本题关系不大：1、即便经过冰河期的不成比例的蒸发，氧16也完全会在某些时候占主要成分(这里的某些时候，不排除指在绝大部分时候，也不排除指在所有时刻)。2、是否可能出现氧16在所有情况下都不占主要成分的可能性呢？不可能，首先在非冰河期就不可能。再者，因为即便在冰河期的某些极端时候出现氧16可能不占主要成分的情况，在非冰河期或冰河衰退的时候，氧16大量回流，氧16对氧18的比例仍会最终回复到氧16占主要成分的程度。]

总之，做题时我们不可能想这么多了。想成“无关”就好了。还是OG中的解释比较好，体现的思维就是：只要是文章承认的基本事实，就不能独立构成对文章的削弱。

Likewise, E would not diminish its usefulness, since isotopic records showing “fluctuations in global ice volume over the past several hundred thousands years” have been sufficient to determine a meaningful pattern (lines 49-53).

If C were shown to be true, Milankovitch’s theory would be weakened, but this would not diminish the value of the isotopic record.

If D were true, researchers would need to accommodate the inconsistency described in evaluating the isotopic record, but, again, this would not compromise the usefulness of the record itself.

谢谢大牛的思路。

wangyu nn 已说得很多，也让我很晕－正在消化中～～

我是菜菜鸟，来发言只是想贴一下OG11 72题中的解释： the lighter isotope does predominate; this is part of the record and does not affect its usefulness

即“重复强调该命题的事实和论据，不能构成对该命题进行削弱的依据”，所以A不对。

是18：16越大，冰越大 ，如果以16为主，应该是冰小，所以说还是有价值的

这篇文章就这块最烦，刚才明白了，突然又糊涂了，转来转去