Day 22

英文重現

Relative land-ice volume for a given period can be deduced from the ratio of two oxygen isotopes,16 and 18, found in ocean sediments… The higher the ratio of oxygen 18 to oxygen 16 in a sedimentary specimen, the more land ice there was when the sediment was laid down.

As an indicator of shifts in the Earth's climate, the isotope record has two advantages. First, it is a global record: there is remarkably little variation in isotope ratios in sedimentary specimens taken from different continental locations. Second, it is a more continuous record than that taken from rocks on land.

——GMAT OG 2015, Reading Comprehension, Passage 15

解析

1.第一個句子的主干為“volume can be deduced from the ratio of two oxygen isotopes”，“16 and 18”是前面名詞“two oxygen isotopes”的同位語，而“found in ocean sediments”是過去分詞作后置定語，修飾前面的“two oxygen isotopes”；倒數第二句中的“taken from different continental locations”也是過去分詞作后置定語，修飾前面的名詞“sedimentary specimens”。

2.“the +比較級，the +比較級”，表示“越……越……”，表示一方的程度隨著另一方的變化而變化，其中的兩個“the”都是副詞，后面必須是形容詞或副詞的比較級。比較的部分可以是表語、狀語，也可以是主語和賓語，這種結構通常是從句在前，主句在后。主句可根據需要調整，采用正常語序或倒裝語序，而從句必須是正常語序，例如：

The noisier they were, the happier was their mother.

他們越吵，他們的媽媽越高興。

此處是形容“land ice”的數量隨著“oxygen 18”與“oxygen 16”的比例高低而變化。

3.第二段中的“as”在這里作介詞，譯為“作為”；當“as”作連詞時，可以引導

從句。

4.最后一句中的“than”后面省略了be動詞“is”。“than”比較的是兩個不同的記錄（來自“different continental locations”和來自“rocks on land”的兩個記錄），這里的“that”為代詞，指代“record”。

詞義辨析

參考翻譯

一定時間內陸地上的冰的數量能夠通過從海洋沉積物中發現的兩種氧同位素——16和18的比例推斷出來……沉積物樣品中氧18/氧16的比例越高，沉積物沉淀時所處的時期就擁有越多的陸地冰。

作為地球氣候變化的一個指標，同位素記錄有兩個優點。一、它是一個全球性的記錄：從不同大陸上采集的沉積物樣品，其同位素比例很少有變化。二、相對于陸地巖石的記錄來說，它是一個更具連續性的記錄。

實戰演練

To establish such a chronology it is necessary to determine the relative amounts of land ice that existed at various times in the Earth's past. A recent discovery makes such a determination possible: relative land-ice volume for a given period can be deduced from the ratio of two oxygen isotopes, 16 and 18, found in ocean sediments. Almost all the oxygen in water is oxygen 16, but a few molecules out of every thousand incorporate the heavier isotope 18. 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. Because heavier isotopes tend to be left behind when water evaporates from the ocean surfaces, the remaining ocean water becomes progressively enriched in oxygen 18. The degree of enrichment can be determined by analyzing ocean sediments of the period, because these sediments are composed of calcium carbonate shells of marine organisms, shells that were constructed with oxygen atoms drawn from the surrounding ocean. The higher the ratio of oxygen 18 to oxygen 16 in a sedimentary specimen, the more land ice there was when the sediment was laid down.

As an indicator of shifts in the Earth's climate, the isotope record has two advantages. First, it is a global record: there is remarkably little variation in isotope ratios in sedimentary specimens taken from different continental locations. Second, it is a more continuous record than that taken from rocks on land…

According to the passage, which of the following is true of the ratios of oxygen isotopes in ocean sediments?

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

(B) They are less reliable than the evidence from rocks on land in determining the volume of land ice.

(C) They can be used to deduce the relative volume of land ice that was present when the sediment was laid down.

(D) They are more unpredictable during an ice age than in other climatic conditions.

(E) They can be used to determine atmospheric conditions at various times in the past.

答案：C

答案解析

由題目中“ratios of oxygen isotopes in ocean sediments”的意思可定位到“A recent discovery makes such a determination possible: relative land-ice volume for a given period can be deduced from the ratio of two oxygen isotopes, 16 and 18, found in ocean sediments”，由此比較容易選出答案C“它們能夠用來推斷出沉淀物在被堆積時陸地上的冰的

數量”，該選項只是將原文的句子順序“A can be deduced from B”改成了“B can be used to deduce A”。

其他選項意思分別為：

A.它們表明，相對于其他時間形成的沉積物來說，冰川時期的沉積物含有更多的碳酸鈣。

B.它們在確定陸地冰的數量方面，沒有從陸地上的巖石中獲得的證據可靠。

D.相對于在其他氣候環境下，它們在冰川時期更加不可預測。

E.它們能夠被用來確定以往不同時期的大氣狀況。