2019年11月2日托福阅读真题+题目+答案：Calcium Carbonate in the Ocean

2019年11月2日托福阅读真题+题目+答案：Calcium Carbonate in the Ocean

Earth's oceans are not uniform. Ocean water near coastlines, for example, contains trace elements of all kinds that help life grow in abundance, whereas the centers of the oceans are typically devoid of life. Ocean chemistry also varies from top to bottom. The surface waters of the ocean are less acidic than the deep ocean because carbon dioxide, which becomes carbonic acid when dissolved in water, is used up as myriad planktonic algae (tiny floating plants) photosynthesize; that is, they use sunlight and carbon dioxide to obtain energy. In those sunlit waters it is easy for some of those planktonic organisms to extract the calcium and carbonate ions with which the water is saturated, and make their intricate, jewel-like calcium carbonate skeletons. As these organisms die, their skeletons fall to the sea floor in their billions to pile up as carbonate deposits. As they fall, they take with them the iron, nitrogen, and phosphorus in their dead tissues. The sunlit surface waters are thus depleted in these elements, which puts a serious brake on further biological growth.   

However, to build carbonate deposits, those tiny skeletons must not sink too deep, for if they do, they will enter a new realm and simply disappear. In the cold, dark depths of the oceans, about 4 kilometers below the sea's surface, the water is both cold and old. Hundreds of years have elapsed since the water has been at the surface--it is charged with carbon dioxide from decaying animal and plant tissues, and part of this gas dissolves to form carbonic acid. As they enter these deep, more acid waters, the calcium carbonate shells simply dissolve and disappear, even before they hit the ocean floor.   。。。。。余下托福阅读真题原文省略！

1. According to paragraph 1, which of the following limits the abundance of life in ocean water near the surface?

A. The presence of trace elements that cause organisms to die

B. The continuous removal of iron, nitrogen, and phosphorus when dead organisms sink

C. The lack of calcium and carbonate particles needed for skeletons

D. The water's saturation with dissolved carbon dioxide

2. According to paragraph 2, which of the following causes the disappearance of calcium carbonate skeletons in deep water?

A. Decay of the skeletons during the hundreds of years they spend at the surface

B. The temperature of the water

C. The calcium carbonate on the ocean floor

D. The presence of carbonic acid in the water

3. According to paragraph 3, how are the skeletons of radiolaria and diatoms different from calcium carbonate skeletons?

A. The skeletons of radiolaria and diatoms can build up even below the CCD.

B. The skeletons of radiolaria and diatoms slowly dissolve in acid waters.

C. The skeletons of radiolaria and diatoms are mainly made of material that comes from desert dust and volcanic ash.

D. The skeletons of radiolaria and diatoms contain large amounts of calcium carbonate.

。。。。。余下托福阅读真题题目省略！

2019年11月2日托福阅读真题+题目+答案：Calcium Carbonate in the Ocean，10元有偿下载完整版！