annieview

如果理解的是意思是说蒸发的水里的18少，那么是不是就意味这16多呢，那多E 是不是也可以选呢？我有不明白~~不知道还有没有人回来

avenue5th

想问下75题，在d和e中不知道选哪个
75. It can be inferred from the passage that calcium carbonate shells
(A)are not as susceptible to deterioration as rocks
(B)are less common in sediments formed during an
(C)are found only in areas that were once covered by land ice
(D)contain radioactive material that can be used to determine a sediment’s isotopic composition
(E)reflect the isotopic composition of the water at the time the shells were formed
A ~e only mention of rocks in the passage is a comparison of “gappiness” of the rock and sedimentary specimen records in lines 38–39; this information does not allow any firm inference to be made with respect to relative susceptibility to deterioration, though a more continuous record might be the result of less susceptibility to deterioration.
B    ~e passage does not make any reference to the relative abundance of these shells during ice ages; no such inference can be drawn.
C ~e only information in the passage that might support this statement is found in lines 29–32, but that information, about the correlation between oxygen ratios in sediment specimens and land ice, describes a relation that implies nothing about distributions of such specimens.
D ~ough the passage does indirectly indicate that the shells contained radioactive material, nothing in the passage suggests that radioactive material is used to determine isotopic composition.
E    Correct. ~e passage explains that oxygen atoms in the surrounding water are one of the building blocks of calcium carbonate shells. ~e isotopic composition of the surrounding water changes during the ice age cycles, so it is logical that the isotopic composition of the shells will change depending on when they were formed.
~e correct answer is E.

elephantsmall

74题，重点还是在这句话：When an ice age begins, the continental ice sheets grow, steadily reducing the amount of water evaporated from the ocean that will eventually return to it.

这句话可以翻译成：当冰期开始时，大陆冰盖开始增长，(这种增长）稳定地减少从海洋里蒸发又以降水形式回到海洋的水的数量（括号里是自己添加的，便于理解）

个人以为，从海洋里蒸发的水之所以会减少，是因为海水蒸发，然后以降水形式变成了大陆冰盖。那么，因为continental ice sheet是经过上述过程而形成的，所以降水中oxygen 18的含量跟continental ice sheet中oxygen 18的含量是相同的。

值得注意的是，虽然蒸发的海水中oxygen 16的含量比较高，但是也会包含一些oxygen 18，而不是一水儿的没有。

一点个人建议，欢迎继续讨论~

elephantsmall

75. It can be inferred from the passage that calcium carbonate shells It can thus be inferred that the shells that make up those sediments must reflect the proportion of oxygen 18 found in the ocean water at the time they were formed.
(A)    are not as susceptible to deterioration as rocks.文章没有针对susceptibility to deterioration做shell与rock的对比。无关。
(B)    are less common in sediments formed during an ice age. NM，文章没有做关于ice age时期shell的情况的说明。
(C)    are found only in areas that were once covered by land ice。文章没有就shells的地点分布做说明。虽然问斩个提到了，shells中氧的比例可以提供当时land ice情况的依据。
(D)    contain radioactive material that can be used to determine a sediment’s isotopic composition. 文章间接的说shells中含有radioactive material（文章提到ratio可以用放射元素测定年代的方法测定。。。），但并没有说这种radioactive material可以被用来测定沉淀的元素组成——它只是可以用一种与放射性物质相关的方法测定氧的比例，也许测不出含有什么其他物质。
(E)    reflect the isotopic composition of the water at the time the shells were formed