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  3. Violent ocean storms in the northern part of the world usually develop in late summer or autumn near the equator. When they happ

Violent ocean storms in the northern part of the world usually develop in late summer or autumn near the equator. When they happ

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问题     Violent ocean storms in the northern part of the world usually develop in late summer or autumn near the equator. When they happen over the northwestern Pacific Ocean, the storms are called typhoons. And, in the eastern Pacific and the Atlantic Ocean, they are called hurricanes. South of the equator, the winds flow in the same direction as the hands on a clock. North of the equator, they flow counter - clockwise.
    Storms can result when the air temperature in one area is different from that of another. Warmer air rises and cooler air falls. These movements create a difference in the pressure of the atmosphere, If the pressure changes over a large area, winds start to blow in a huge circle. High - pressure air is pulled into a low - pressure center. Storms can get stronger and stronger as they move over warm ocean waters. Up to 50 centimeters of rain can fall. Some storms have produced more than 150 centimeters of rain.
    The scale is divided into 5 categories. A category one storm has winds of about 120 to 150 kilometers an hour. It can damage trees and lightweight structures. Wind speeds in a category two hurricane can reach close to 180 kilometers an hour. These storms are often powerful enough to break windaws or blow the roof off a house. Winds between about 180 and 250 kilometers an hour represent categories three and four. Anything even more powerful is a category five hurricane. The researchers say that about 35% of all hurricanes in the past ten years were category four or five.
    Weather scientists call hurricanes by names to make clear just which storm they are talking about, especially when two or more take place at the same time. They say using short names is especially important when exchanging storm information among weather stations and ships at sea. Weather scientists used the names of their girlfriends or wives for storms during World War Two. The United States weather service started officially using women’s names for storms in 1953. In 1978, realizing the sex prejudice of such names, it began including men’s names as well.
The first paragraph mainly_____.
选项 A、tells us the areas where hurricanes come about
B、confirms the position of typhoons
C、gives clear definitions of violent ocean storms
D、explains the different changes near the equator
答案C
解析 开篇就提出violent ocean storms，故答案为C。
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