Day 23

英文重現

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.

——GMAT OG 2015, Reading Comprehension, Passage 15

解析

1.現在分詞可以充當狀語，表示主句動作發生后造成的結果，比如“He fired, killing one of the birds on the tree”，打死了樹上的一只鳥就是開槍的后果。第一句中的“steadily reducing…return to it”也是充當狀語，說明冰原變大后的結果；“evaporated from the ocean”則是過去分詞作后置定語，與后面的從句“that will eventually return to it”一起修飾前面的名詞“water”（“it”指代“ocean”）。

2.第二個句子中，“when”引導的時間狀語從句“when water evaporates from the ocean surfaces”修飾“tend”；主句中的詞組“become enriched in”意思是“變得富含……”。

詞義辨析

參考翻譯

當冰川期開始后，大陸冰原會變大，持續地減少從海洋中蒸發并最終返回海里的水量。因為當水從海洋表面蒸發時，較重的同位素通常會被留下來，所以剩下的海水會逐漸變得富含氧18。

實戰演練

…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 precipitation formed from evaporated ocean water has

(A) the same isotopic ratio as ocean water.

(B) less oxygen 18 than does ocean water.

(C) less oxygen 18 than has the ice contained in continental ice sheets.

(D) a different isotopic composition than has precipitation formed from water on land.

(E) more oxygen 16 than has precipitation formed from fresh water.

答案：B

答案解析

題目問的是從海洋中蒸發的水形成的降水包含什么，從選項可推出題目問的應該是蒸發的海洋水的氧元素組成。根據“precipitation formed evaporated ocean water”的意思可以定位到“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”（海水蒸發后通過降雨的形式回到陸地），根據這一個句子我們無法直接獲得答案，但是其后的“because”一句闡述了一個原理“當水從海洋表面蒸發時，較重的同位素通常會被留下來，所以剩下的海洋水包含的氧18會越來越多”（因為氧18比較重），由此可推斷出“蒸發了的海洋水中包含的氧18比較少”，從而得出正確選項為B“（蒸發的海洋水）比海洋水含有更少的氧18”。

選項A“（蒸發的海洋水）和海洋水的氧元素比例相同”錯誤。從文中所給的信息，我們并不知道“ice contained in continental ice sheets”、“precipitation formed from water on land”和“precipitation formed from fresh water”的氧元素構成，因此排除選項C“（蒸發的海洋水）比大陸冰川的冰含有更少的氧18”、選項D“（蒸發的海洋水）的氧元素組成與從陸地水形成的降水是不同的”以及選項E“（蒸發的海洋水）比淡水形成的降水含有更多的氧16”。