[单项选择]Today’s lecture is about two powerful natural forces, one destructive, yet the other productive.
Tornado (龙卷风) is a typical example of destructive forces in nature. Forces other than damaging winds are also at work inside tornadoes. Sometimes as twisting, screaming wind passes over house, the walls and the ceiling burst apart as if a bomb had gone off inside. This explosion is caused by the low air pressure at the center of a tornado.
The pressure at the center of a tornado is usually 13 pounds per square inch. However, inside the house the air pressure is normal, about 15 pounds per square inch. The difference of 2 pounds per square inch between the inside and outside pressure may not seem like much. But suppose a tornado passes over a small building that measures 20 by 10 feet. On each square inch of the building, there is 2 pounds of pressure from the inside that is not balanced by air pressure outside the building. On the ceiling, that adds up to an unbalanced pressu
A. force of tornado increases the air pressure in a building
B. air pressure at the center of a tornado is as strong as over 172,000, pounds
C. weight of a tornado can crush a building’s roof when it passes overhead
D. air pressure inside a tornado is less than air pressure inside a building

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[单项选择]Today’s lecture is about two powerful natural forces, one destructive, yet the other productive.
Tornado (龙卷风) is a typical example of destructive forces in nature. Forces other than damaging winds are also at work inside tornadoes. Sometimes as twisting, screaming wind passes over house, the walls and the ceiling burst apart as if a bomb had gone off inside. This explosion is caused by the low air pressure at the center of a tornado.
The pressure at the center of a tornado is usually 13 pounds per square inch. However, inside the house the air pressure is normal, about 15 pounds per square inch. The difference of 2 pounds per square inch between the inside and outside pressure may not seem like much. But suppose a tornado passes over a small building that measures 20 by 10 feet. On each square inch of the building, there is 2 pounds of pressure from the inside that is not balanced by air pressure outside the building. On the ceiling, that adds up to an unbalanced pressu
A. dosing the cellar
B. opening the window
C. using a fan for air circulation
D. strengthening the roof and walls

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[单项选择]There is much discussion today about whether economic growth is desirable. At an earlier period, our desire for material wealth may have been justified. Now, howerer, this desire for more than we need is causing serious problems. Even though we have good intentions, we may be producing too much, too fast.
Those who criticize economic growth argue that we must slow down. They believe that society is approaching certain limits on growth. These include the fixed supply of natural resources, the possible negative effects of industry on the natural environment, and the continuing increase in the world’s population. As society reaches these limits, economic growth can no longer continue, and the quality of life will decrease.
People who want more economic growth, on the other hand, argue that even at the present growth rate there are still many poor people in the world. These proponents of economic growth believe that only more growth can create the capital needed to improve the qu
A. Even though economy grows at the present rate, poverty still exists in the world.
B. Economy must grow because poverty still exists.
C. The present rate of economic growth is too slow.
D. Economic growth may produce the money needed to get rid of poverty throughout the world

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