Day 24

英文重現(xiàn)

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.

——GMAT OG 2015, Reading Comprehension, Passage 15

解析

“shells that were constructed...surrounding ocean”是前面“calcium carbonate shells”的同位語；“that”引導(dǎo)的定語從句修飾“shells”，其中“drawn from the surrounding ocean”是過去分詞短語作后置定語，修飾前面的“oxygen atoms”，意思上相當(dāng)于定語從句“which were drawn from the surrounding ocean”。

詞義辨析

參考翻譯

（前兩句的翻譯見Day 23） （氧18的）豐富程度能夠通過分析當(dāng)時的海洋沉積物來確定，因為這些沉積物是由海洋生物的碳酸鈣外殼組成的，這些外殼由從周圍海洋中吸收的氧原子構(gòu)造而成。

實戰(zhàn)演練

…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.

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 ice age.

(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.

答案：E

答案解析

由題目中“calcium carbonate shells”定位到“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”，關(guān)鍵要理解“shells that were constructed with oxygen atoms drawn from the surrounding ocean”中的“shells”是“calcium carbonate shells”的同位語，由本句話可以知道“碳酸鈣外殼是由從周圍海洋中吸收的氧原子構(gòu)造的”，因此可以得出正確選項為E“（碳酸鈣外殼）可以反映出外殼形成時水體中氧元素的構(gòu)成”。其他選項在文中均未提到，意思分別為：

A.（碳酸鈣外殼）不像巖石那樣容易變質(zhì)。

B.（碳酸鈣外殼）在冰川時期形成的沉積物中不太常見。

C.（碳酸鈣外殼）只有在曾經(jīng)被陸地冰覆蓋的地區(qū)才能被發(fā)現(xiàn)。

D.（碳酸鈣外殼）含有放射性材料，這些放射性材料能夠被用來確定沉積物的氧元素構(gòu)成。