Space is a dangerous place, not only because of meteors(流星), but also because of rays from the sun and other stars. The atmosphere again acts as our protective blanket on the earth. Light gets through, and this is necessary for plants to make the food which we eat. Heat, too, makes our environment suitable to live. Various kinds of rays come through the air from outer space, but enormous quantities of radiation from the sun are screened off. As soon as men leave the atmosphere they are exposed to this radiation but their spacesuits or the walls of their spacecraft, if they are inside, do prevent a lot of radiation damage.

Radiation is the greatest known danger to explorers in space. The unit of radiation is called “rem”. Scientists have reason to think that a man can put up with far more radiation than 0.1 rem without being damaged; the figure of 60 rems has been agreed on. The trouble is that it is extremely difficult to be sure about radiation damage a person may feel perfectly well, but the cells of his or her sex organs may be damaged, and this will not be discovered until the birth of deformed(畸形的)children or even grandchildren. Missions of the Apollo flights have had to cross belts of high radiation and, during the outward and return journeys, the Apollo crew accumulated a large amount of rems. So far, no dangerous amounts of radiation have been reported, but the Apollo missions have been quite short. We simply do not know yet how men are going to get on when they spend weeks and months outside the protection of the atmosphere, working in a space laboratory. Drugs might help to decrease the damage done by radiation, but no really effective ones have been found so far.

49．According to the first paragraph, the atmosphere is necessary to man because of the following reason EXCEPT________

A．protecting him against the harmful rays from space

B．providing sufficient light for plant growth

C．suppling the heat necessary for human survival

D．screening off the falling meteors

50．We learn from the passage that ________

A．exposure to even tiny amounts of radiation is fatal

B．the effect of exposure to radiation is slow in coming

C．radiation is avoidable in space exploration

D．astronauts in spacesuits needn’t worry about radiation damage

51．The harm radiation that has been done to the Apollo crew members ________

A．is insignificant   B．is enormous   C．seems overestimated  D．remains unknown

52．It can be inferred from the passage that________

A．the Apollo mission was very successful

B．the protection from space radiation is no easy job

C．astronauts may possibly have deformed children or grandchildren

D．radiation is not a threat to well-protected space explorers

53．Which of the following is TRUE?

A．Space is dangerous only because of meteors.

B．Explorers in space have to avoid the damage from radiation

C．We have got effective ways to treat illnesses caused by radiation.

D．The atmosphere doesn’t screen off radiation

Space is a dangerous place, not only because of meteors(流星), but also because of rays from the sun and other stars. The atmosphere again acts as our protective blanket on the earth. Light gets through, and this is necessary for plants to make the food which we eat. Heat, too, makes our environment suitable to live. Various kinds of rays come through the air from outer space, but enormous quantities of radiation from the sun are screened off. As soon as men leave the atmosphere they are exposed to this radiation but their spacesuits or the walls of their spacecraft, if they are inside, do prevent a lot of radiation damage.

Radiation is the greatest known danger to explorers in space. The unit of radiation is called “rem”. Scientists have reason to think that a man can put up with far more radiation than 0.1 rem without being damaged; the figure of 60 rems has been agreed on. The trouble is that it is extremely difficult to be sure about radiation damage a person may feel perfectly well, but the cells of his or her sex organs may be damaged, and this will not be discovered until the birth of deformed(畸形的)children or even grandchildren. Missions of the Apollo flights have had to cross belts of high radiation and, during the outward and return journeys, the Apollo crew accumulated a large amount of rems. So far, no dangerous amounts of radiation have been reported, but the Apollo missions have been quite short. We simply do not know yet how men are going to get on when they spend weeks and months outside the protection of the atmosphere, working in a space laboratory. Drugs might help to decrease the damage done by radiation, but no really effective ones have been found so far.

49．According to the first paragraph, the atmosphere is necessary to man because of the following reason EXCEPT________

A．protecting him against the harmful rays from space

B．providing sufficient light for plant growth

C．suppling the heat necessary for human survival

D．screening off the falling meteors

50．We learn from the passage that ________

A．exposure to even tiny amounts of radiation is fatal

B．the effect of exposure to radiation is slow in coming

C．radiation is avoidable in space exploration

D．astronauts in spacesuits needn’t worry about radiation damage

51．The harm radiation that has been done to the Apollo crew members ________

A．is insignificant   B．is enormous   C．seems overestimated  D．remains unknown

52．It can be inferred from the passage that________

A．the Apollo mission was very successful

B．the protection from space radiation is no easy job

C．astronauts may possibly have deformed children or grandchildren

D．radiation is not a threat to well-protected space explorers

53．Which of the following is TRUE?

A．Space is dangerous only because of meteors.

B．Explorers in space have to avoid the damage from radiation

C．We have got effective ways to treat illnesses caused by radiation.

D．The atmosphere doesn’t screen off radiation

   Global warming is when the earth heats up, the temperature rises. It happens when greenhouse gases ---carbon dioxide, water vapor, nitrous oxide(二氧化氮), and methane(沼气) trap heat and light from the sun in the earth’s atmosphere, which increases the temperature. This is like when heat is trapped in a car. On a very hot day, the car gets hotter when it is out in the parking lot. This is because the heat and light from the sun can get into the car, by going through the windows, but it can’t get back out. Once the light is inside the car, it is trapped and the heat builds up, just like it does in the earth’s atmosphere. This is what the greenhouse effect does to the earth. The heat and light can get through the atmosphere, but it can’t get out. As a result, the temperature rises.

   Sometimes the temperature can change in a way that helps us. The greenhouse effect makes the earth appropriate for people to live on. Without it, the earth would be freezing, or on the other hand it would be burning hot. We would not get the sun’s heat and light to make the night somewhat warm. During the day, especially during the summer, it would be burning because the sun would be up with no atmosphere to filter(过滤) it, so people, plants, and animals would be exposed to all the light and heat.

  Although the greenhouse effect makes the earth able to have people living on it, if there gets to be too many gases, the earth can get unusually warmer, and many plants, animals, and people will die. They would die because there would be less food(plants like corn, wheat, and other vegetables and fruits). This would happen because the plants would not be able to take in the heat. This would cause us to have less food to eat, but it would also limit the food that animals have. Gradually, people, plants, and animals would all die of hunger.

   People are doing many things to try stop global warming. One thing people are doing is carpooling. Carpooling is driving with someone to a place that you are both going to. This minimizes the amount of greenhouse gases put into the air by a car. Another thing that people are doing is being more careful about leaving things turned on like the television, computer, and the lights. A lot of people are taking time away from the television, and instead, they are spending more time outdoors. This helps our planet out a lot. Now, more people are even riding buses, walking to school, and riding their bikes to lower the amount of greenhouse gases in the air.

   Planting trees and recycling also help. If you recycle, less trash goes to the dump, and less trash gets burned. As a result, there are fewer greenhouse gases in our atmosphere. Although adults do many things to help stop global warming, kids can do just as much.

68. By the example given in paragraph 1, the author wants to _______.

A. say that there are greenhouse gases in every car

B. show his feeling in a car in hot summer

C. tell us cars are causes of greenhouse gases

D. explain how greenhouse gases work

69. What is the effect of atmosphere?

A. It only traps the heat of the sun.

B. It makes the earth neither too hot nor too cold.

C. It works the same way as greenhouse gases.

D. It prevents all the light from the sun shining on the earth.

70. What is the main idea of the third paragraph?

A. Although greenhouse effect is necessary, too much of it causes us to die.

B. Human beings are likely to disappear from the earth.

C. Crops can’t take the heat if there is greenhouse effect.

D. If there is greenhouse effect, all the plants will die.

71. What will the author most probably discuss in the paragraph that follows?

A. Why cars and buses pollute the air a lot.

B. What global warming is doing to the environment.

C. What kids can do to help stop global warming.

D. Who should be responsible for the environmental problems.

Global warming is when the earth heats up，the temperature rises.It happens when greenhouse gases—carbon dioxide，water vapor，nitrous oxide(二氧化氮)，and methane(沼气) trap heat and light from the sun in the earth’s atmosphere，which increases the temperature.This is like when heat is trapped in a car.On a very hot day，the car gets hotter when it is out in the parking lot.This is because the heat and light from the sun can get into the car，by going through the windows，but it can’t get back out.Once the light is inside the car，it is trapped and the heat builds up，just like it does in the earth’s atmosphere.This is what the greenhouse effect does to the earth.The heat and light can get through the atmosphere，but it can’t get out.As a result，the temperature rises.

Sometimes the temperature can change in a way that helps us.The greenhouse effect makes the earth appropriate for people to live on.Without it，the earth would be freezing，or on the other hand it would be burning hot.We would not get the sun’s heat and light to make the night somewhat warm.During the day，especially during the summer，it would be burning because the sun would be up with no atmosphere to filter(过滤) it，so people，plants，and animals would be exposed to all the light and heat.

Although the greenhouse effect makes the earth able to have people living on it，if there gets to be too many gases，the earth can get unusually warmer，and many plants，animals，and people will die.They would die because there would be less food (plants like corn，wheat，and other vegetables and fruits)．This would happen because the plants would not be able to take in the heat.This would cause us to have less food to eat，but it would also limit the food that animals have.Gradually，people，plants，and animals would all die of hunger.

People are doing many things to try to stop global warming.One thing people are doing is carpooling.Carpooling is driving with someone to a place that you are both going to.This minimizes the amount of greenhouse gases put into the air by a car.

Another thing that people are doing is being more careful about leaving things turned on like the television，computer，and the lights.A lot of people are taking time away from the television，and instead，they are spending more time outdoors.This helps our planet out a lot.Now，more people are even riding buses，walking to school，and riding their bikes to lower the amount of greenhouse gases in the air.

Planting trees and recycling also help.If you recycle，less trash goes to the dump，and less trash gets burned.As a result，there are fewer greenhouse gases in our atmosphere.Although adults do many things to help stop global warming，kids can do just as much.

1.By the example given in Paragraph 1，the author wants to ________.

A．explain how greenhouse gases work

B．show his feeling in a car in hot summer

C．tell us cars are causes of greenhouse gases

D．say that there are greenhouse gases in every car

2.The underlined word “it” in Paragraph 2 refers to “________”．

A．light? B．heat

C．temperature? D．greenhouse effect

3.What is the main idea of Paragraph 3?

A．If there is greenhouse effect，all the plants will die.

B．Human beings are likely to disappear from the earth.

C．Crops can’t take the heat if there is greenhouse effect.

D．Although greenhouse effect is necessary，too much of it causes us to die.

4.What will the author most probably discuss in the paragraph that follows?

A．Why cars and buses pollute the air a lot.

B．What kids can do to help stop global warming.

C．What global warming is doing to the environment.

D．Who should be responsible for the environmental problems.