[originaltext]W: Dr. Smith. I need to ask you about something in Chapter 12. We

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问题  
W: Dr. Smith. I need to ask you about something in Chapter 12. Well, it talks about erosion and the de posit of sediment(solid matter that settles at the bottom of a liquid)on the deep sea floor, but I’m confused. For that to happen, there would have to be some kind of force down there moving the mud or sand or whatever, right? But I thought there weren’t any waves or currents that deep in the ocean.
M: That’s not exactly correct. It’s true that deep down on the ocean floor we won’t have the same kinds of currents we find in shallower parts. But we do find what we call turbidity currents. This wasn’t in the book but the term came up in class. Do you remember what it means?
W: Umh, turbidity currents? Oh, yeah! Isn’t that when sediment like sand or mud gets stirred up and mixes with water. And then this mixture flows through the water around it, right?
M: Good !
W: Uhe, but I thought that only happened in rivers.
M: Well, yes. This does occur in rivers, but we see turbidity currents deep in the ocean as well.
W: But how do they get started there?
M: Earthquakes mostly, when an earthquake occurs under water, it throws up tremendous amounts of mud or sand that becomes suspended in a layer of water near the bottom of the ocean. This layer is so much denser and heavier than other ocean water that if flows right down the slopes of the ocean floor and gains more and more speed as it moves along. Then it’s just like the winds blowing across the desert picking up sand from one place and moving it along and finally dropping it somewhere else.

选项 A、To explain the effects of turbidity currents.
B、To explain how winds cause turbidity currents.
C、To remind the student about the next assignment.
D、To remind the student where ocean sediments originate.

答案 A

解析 推理题。短文在提及地震带动海底底层(layer)的泥沙沉淀物运动状态时提及desert winds带动沙的运动状态,两者之间的共同点是都在运动过程中带动泥或者沙的沉淀物,这个特征也正是turbidity currents运动时所具有的特征,所以提及desert winds的运动特征能解释turbidity cur rents所带来的影响。
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