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Forces other than damaging winds are also at work inside tornadoes. Sometimes, as the writhing, 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 angin ribut.

The pressure at the center of a topan 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 funnel passes over a small building that measures 20 by 10 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 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 outside 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, badai cellars must have an air vent. Otherwise, the cellar door might be blown out when a tornado passes over it.

1. Which of the following is the main topic of the passage?

(A) How tornadoes can be prevented (B) When tornadoes usually occur

2. In line 2, the word "funnel" refers to which of the following?

(A) A bomb (B) A house (C) A tornado (D) An explosion

3. According to the passage, tornadoes can destroy buildings because the

(A) force of a badai increases the air pressure in a building

(B) air pressure at the center of a tornado is over 172,000 pounds

(D) air pressure inside a angin ribut is less than the air pressure inside a building

4. According to the passage, what is the difference per square inch between the air pressure inside a building and the air pressure inside a tornado?

(A) 2 pounds (B) 10 pounds (C) 13 pounds (D) 15 pounds

5. According to the passage, the pressure on a building during a badai can be relieved by

(A) closing the cellar (B) opening the windows

6. According to the passage, people close their windows to prevent damage caused by

(A) tornadoes (B) thunderstorms

7. In line 17, the word "it" refers to

(A) wind (B) hail (C) cellar door (D) air vent

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