Force other than damaging winds are also at work inside tornadoes. Sometimes, as the turning, jumping funnel(漏斗) passes over a house, the walls and ceiling burst apart as if a bomb had gone off inside. This explosion(爆炸) 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 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 great inside pressure may cause the building to burst.

　　Unfortunately, heavy rain happens in thunderstorms that later produce tornadoes. So, people often shut all windows to protect their property. This may cause far worse damage later.

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

A. Where tornadoes are formed. 　　      B. When tornadoes usually occur.

C. How tornadoes can be prevented.　　     D. Why tornadoes cause so much damage.

64. According to the passage, tornadoes can destroy building because the _____.

A. force of a tornado increases the air pressure in a building

B. air pressure at the center of a tornado is 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 the air pressure inside a building

65. According to the passage, the pressure on a building during a tornado can be reduced　　　　by _____.

A. closing the windows 　　　　　        B. opening the windows

C. using an electric fan 　　　　          D. making the roof and walls stronger

Force other than damaging winds are also at work inside tornadoes. Sometimes, as the turning, jumping funnel(漏斗) passes over a house, the walls and ceiling burst apart as if a bomb had gone off inside. This explosion(爆炸) 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 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 great inside pressure may cause the building to burst.

　　Unfortunately, heavy rain happens in thunderstorms that later produce tornadoes. So, people often shut all windows to protect their property. This may cause far worse damage later.

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

A. Where tornadoes are formed.  　　      B. When tornadoes usually occur.

C. How tornadoes can be prevented.　　     D. Why tornadoes cause so much damage.

64. According to the passage, tornadoes can destroy building because the _____.

A. force of a tornado increases the air pressure in a building

B. air pressure at the center of a tornado is 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 the air pressure inside a building

65. According to the passage, the pressure on a building during a tornado can be reduced　　　　by _____.

A. closing the windows 　　　　　        B. opening the windows

C. using an electric fan 　　　　          D. making the roof and walls stronger

Trains were used for long distance transportation.

Today the car is the most   1   sort of transportation in all of the   2  .It has completely taken the place of the horse as a   3  of  everyday transportation. The Americans use their cars for nearly 90   4   all their   5  .Most Americans are   6   to buy cars. The average(平均)   7   of a car was 2050 in 1950,2740 in 1960 and up to 4750 in 1975. During this period, American carmakers   8   improving their products. As a   9  ,the income of the average family   10   from 1950 to 1970   11   than the price of cars.  12  ,buying a new car takes a smaller part of a family’s   13   income today. In 1951, it   14   8.1 months of an average family’s income to buy a new car. In 1962,a new car   15   6.43 months of a family’s income. By 1975,it   16   took 4.75 months’ income.  17  ,the 1975 cars were technically   18   than those of the previous(先前的)   19  .

That’s why cars are so   20   in the USA.

1.A.useful　　　　　　　　　　 B.valuable　　　　　　　　　　 C.cheap　　　　　　　　　　    D.popular

2.A.United States 　　　　 B.world 　　　　　　　　　　  C.year　　　　　　　　　　　　  D.continent

3.A.development　　　　   B.journey　　　　　　　　　　  C.sign　　　　　　　　　　　　  D.means

4.A.percent　　　　　　　　   B.years　　　　　　　　  　　   C.miles　　　　　　　　　　　　 D.dollars

5.A.trips　　　　　　　　　　   B.lives　　　　　　　　　　　　  C.buissness　　　　　　　　  D.time

6.A.permitted　　　　　　    B.encouraged　　　　　　    C.anxious　　　　　　　　　　 D.able

7.A.value　　　　　　　　　　  B.cost　　　　　　　　　　　　  C.price　　　　　　　　　　　　 D.money

8.A.suggested　　　　　　   B.enjoyed 　　　　　　　　    C.made up　　　　　　　　    D.started

9.A.tool　　　　　　　　　　    B.result　　　　　　　　　　    C.drive　　　　　　　　　　　　 D.producer

10.A.reduced　　　　　　    B.increased　　&n

bsp;　　　　　　  C.received　　　　　　　　    D.needed

11.A.more slowly　　　　  B.smaller　　　　　　　　　　  C.faster　　　　　　　　　　    D.less

12.A.However　　　　　　   B.For example　　　　　　   C.Instead　　　　　　　　　　  D.For this reason

13.A.low　　　　　　　　　　  B.high　　　　　　　　　　　　  C.monthly　　　　　　　　    D.total

14.A.needs　　　　　　　　   B.took　　　　　　　　　　　　  C.spent　　　　　　　　　　    D.saved

15.A.spent　　　　　　　　    B.paid　　  　　　　　　    C.cost　　 　　　　　　　　 D.took

16.A.might    　　　　    B.really    　　　　　　　　  C.only　　 　　　　　　　　 D.would

17.A.Otherwise  　　　　 B.Besides　　　　　　   C.But　　  　　　　　　　　 D.Finally

18.A.improved   　　　　 B.better　　　　　　　　　　    C.lighter  　　　　　　　　    D.smaller

19.A.months　　 　　    B.years    　　　　　　　　  C.cars　　 　　　　　　　　 D.families

20.A.popular    　　　　  B.expensive　　　　　　　　  C.cheap   　　　　　　　　  D.good

Force other than damaging winds are also at work inside tornadoes. Sometimes, as the turning, jumping funnel(漏斗) passes over a house, the walls and ceiling burst apart as if a bomb had gone off inside. This explosion(爆炸) 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 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 great inside pressure may cause the building to burst.
　　Unfortunately, heavy rain happens in thunderstorms that later produce tornadoes. So, people often shut all windows to protect their property. This may cause far worse damage later.
63. Which of the following is the main topic of the passage?
A. Where tornadoes are formed. 　　      B. When tornadoes usually occur.
C. How tornadoes can be prevented.　　     D. Why tornadoes cause so much damage.
64. According to the passage, tornadoes can destroy building because the _____.
A. force of a tornado increases the air pressure in a building
B. air pressure at the center of a tornado is 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 the air pressure inside a building
65. According to the passage, the pressure on a building during a tornado can be reduced　　　　by _____.
A. closing the windows 　　　　　        B. opening the windows
C. using an electric fan 　　　　          D. making the roof and walls stronger