公共英语考试

【单选题】Forces other than damaging winds are also at work inside tornadoes. Sometimes, as the twisting funnel passes over a house, the walls and 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, a bout 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 funnel 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 pres sure outside the building. On the ceiling, that adds up to an unbalanced pressure of 57 600 pounds. The pressure on the four walls adds up to 172 800 pounds.
If windows are open in the building, some of the inside air will rush out through them. This will balance the pressure inside and out side the building.But if the windows are shut tightly, the enormous inside pressure may cause the building to burst. Unfortunately, heavy rain and hail often occur in thunderstorms that later produce tornadoes. So people frequently shut all windows to protect their property. This may cause far worse damage later. For the same reason, tornado cellars must have an air vent. Otherwise, the cellar door might be blown out when a tornado passes over it.
According to the passage, the pressure on a building during a tor nado can be relieved by______.A．opening the windows
B．closing the windows
C．strengthening the roof and walls
D．using a fan

网考网参考答案：A
网考网解析：
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