It was once thought that air pollution affected only the area around large urban districts with factories and heavy automobile traffic. Today, we know that although these are the areas with the worst air pollution, the problem is literally(=really) worldwide. On several occasions over the past decade, a heavy cloud of air pollution has covered the entire eastern half of the United States and led to health warnings even in rural areas away from any major concentration of manufacturing（制造业的） and automobile traffic. In fact, the very climate of the entire earth may be affected by air pollution. Some scientists feel that the increasing concentration of carbon dioxide in the air resulting from the burning of fossil fuels is creating a “greenhouse effect” holding in heat reflected from the earth and raising the world’s average temperature. If this view is correct and the world’s temperature is raised only a few degrees, much of the polar ice cap will melt and cities such as New York, Boston, Miami, and New Orleans will be under water.

Another view, less widely held, is that increasing particulate matter（颗粒物质）in the atmosphere is blocking sunlight and lowering the earth’s temperature a result that would be equally disastrous（损失惨重的）. A drop of just a few degrees could create something close to new ice age and would make agriculture difficult or impossible in many of our top farming areas. At present we do not know for sure that either of these conditions will happen (though one recent government report prepared by experts in the field concluded that the greenhouse effect is very likely). Perhaps, if we are very lucky, the two tendencies will offset each other and the world’s temperature will stay about the same as it is now.

51. As pointed out at the beginning of the passage, people used to think that air pollution       .

       A. caused widespread damage in the countryside

       B. affected the entire eastern half of the United States

       C. had damaging effects on health

       D. existed merely in urban and industrial areas

52. As far as the greenhouse effect is concerned, the author       .

       A. shares the same view with the scientists

       B. is uncertain of its occurrence

       C. rejects it as being ungrounded

       D. thinks that it will destroy the world soon

53. The word “offset” (Para. 2) could best be replaced by       .

       A. slip into                B. make up for          C. set up                   D. catch up with

54. It can be inferred from the passage that           .

       A. raising the world’s temperature only a few degrees wouldn’t do much harm to life on earth

       B. lowering the world’s temperature merely a few degrees would lead many major farming areas to disaster

       C. almost no temperature variations have occurred over the past decade

       D. the world’s temperature will remain constant in the years to come

55. This passage is primarily concerned with       .

       A. the greenhouse effect                            B. the burning of fossil fuels

       C. the potential effect of air pollution           D. the likelihood of a new ice age

Climatic conditions are delicately adjusted to composition of the Earth's atmosphere. If there were a change in the atmosphere ― for example, in the relative amounts of atmospheric gases ― the climate would probably change also. A slight increase in water vapor (蒸汽) , for example, would increase the heat-keeping capacity of the atmosphere and would lead to a rise in global temperatures.

The level of carbon dioxide, CO₂, in the atmosphere has an important effect on climatic change. Most of the Earth's incoming energy is short-wavelength radiation (短波辐射) , which tends to pass through atmospheric CO₂ easily. The Earth, however, reradiates much of the received energy as long-wavelength radiation (长波辐射), which CO₂ absorbs and then goes toward the Earth. This phenomenon, known as the greenhouse effect, can result in an increase in the surface temperature of a planet. An extreme example of the effect is shown by Venus, a planet covered by heavy clouds composed mostly of CO₂, whose surface temperatures have been measured at 430~C.If the CO₂ content of the atmosphere is reduced, the temperature falls. According to one respectable theory, if the atmospheric CO₂ concentration were halved, the Earth would become completely covered with ice.  Another equally respectable theory, however, states that a halving of the CO₂ concentration would lead only to a reduction in global temperatures of 3℃.

If, because of an increase in forest fires or volcanic activity, the CO₂ content of the atmosphere increased, a warmer climate would be produced. Plant growth, which relied on both the warmth and the availability of CO₂, would probably increase. As a consequence, plant would use more and more CO₂.  Eventually CO₂ levels would decrease and the climate, in turn, would become cooler. With reduced temperatures many plants would die; CO₂ would thus be returned to the atmosphere and gradually the temperature would rise again. Thus, if this process occurred, there might be a long-term oscillation (波动) in the amount of CO₂ present in the atmosphere, with regular temperature increase and decrease.

Some climatologists argue that the burning of fossil fuels has raised the level of CO₂ in the atmosphere and has caused a global temperature increase of at least 1℃. But a supposed global temperature rise of 1 ℃ may in reality be only several regional temperature increases, restricted to areas where there are many meteorological (气象的) stations. Other areas, for example, the Southern Hemisphere oceanic zone, may be experiencing an equal temperature decrease that is unrecognized because of the shortage of meteorological recording stations.

51. Which of the following questions does the information supplied in this passage try to answer?

A. What are the steps in the process that takes place as CO₂ absorbs long-wavelength radiation?

B. How might our understanding of the greenhouse effect be improved if the burning of fossil  were decreased?

C. What might cause a series of regular increases and decreases in the amount of CO₂ in the atmosphere?

D. Why are there fewer meteorological recording stations in the Southern Hemisphere oceanic zone than atmosphere?

52. The author is primarily concerned with ________.

A. explaining the effects that the burning of fossil fuels might have on climate

B. explaining the effects of CO₂ on atmospheric radiation

C. discussing effects that changes in the CO₂ level in the atmosphere might have on climate

D. challenging hypotheses (假说)  about the effects of water vapor and CO₂ on climate

53. The passage suggests that a large decrease in the amount of CO₂ in the atmosphere would result in _________.

A. at least a slight decrease in global temperatures

B. at the most a slight increase in short-wavelength radiation reaching the Earth

C. a slight long-term increase in global temperatures

D. a slight short-term increase in atmosphere water vapor content

54. The author refers to Venus primarily in order to _______.

A. show that the greenhouse effect works on other planets but not on Earth

B. show the degree to which Earth's atmosphere differs from that of Venus

C. support the opinion that as water vapor increases, the amount of CO₂ increases

D. support the argument that the CO₂ level in the atmosphere has a significant effect on climate

55. The discussion of climate in the passage suggests that _________.

A. climate is perfectly stable

B. we are unable at present to measure global temperature changes precisely.

C. the only cause of regional climatic fluctuations (波动) is the change in CO₂ 1evel in the atmosphere

D. slight regional temperature changes can be considered an abnormal feature (特征) of the environment

It was once thought that air pollution affected only the area immediately around large cities with factories and/or heavy automobile traffic. Today, we know that although these are the areas with the worst air pollution, the problem is literally worldwide. On several occasions over the past decade, a heavy cloud of air pollution has covered the entire eastern half of the United States and led to health warnings even in rural areas away from any major concentration of manufacturing and automobile traffic. In fact, the very climate of the entire earth may be affected by air pollution. Some scientists feel that the increasing concentration of carbon dioxide in the air resulting from the burning of fossil fuels（coal and oil） creating a greenhouse effect-holding in heat reflected from the earth and raising the world’s average temperature. If this view is correct and the world’s temperature is raised only a few degrees, much of the polar ice cap will melt and cities such as New York, Boston, Miami, and New Orleans will be under water.

Another view, less widely held, is that increasing particulate matter in the atmosphere is blocking sunlight and lowering the earth’s temperature-a result that would be equally disastrous（灾难的）. A drop of just a few degrees could create something close to a new ice age, and would make agriculture difficult or impossible in many of our top farming areas. At present we do riot know for sure that either of these conditions will happen（though one recent government report prepared by experts in the field concluded that the greenhouse effect is very likely）. Perhaps, if we very lucky, the two tendencies will offset each other and the world’s temperature will stay about the same as it is now.

1．As pointed out at the beginning of the passage, people used to think that air pollution ______.

      A．caused widespread damage in the countryside

      B．affected the entire eastern half of the United States

      C．almost brought worldwide effect

      D．existed merely in urban and industrial areas

2．As far as the greenhouse effect is concerned, the author _____________.

      A．shares the same view with the scientists

      B．is uncertain of its occurrence

      C．rejects it as being ungrounded（无根据的）

      D．thinks that it will increasingly destroy the world soon

3．It can be inferred from the passage that                    .

      A．raising the world’s temperature a little would not do much harm to life on the earth

      B．lowering the world’s temperature a little would lead to agricultural disasters

      C．almost no temperature variations have occurred over the past decade

      D．the world’s temperature will remain stable forever

4．This passage is primarily concerned with              .

      A．the greenhouse effect in the world

      B．the measures to adjust the climate

      C．the potential effect of air pollution

      D．the measures to protect the environment

It was once thought that air pollution affected only the area immediately around large cities with factories and/or heavy automobile traffic. Today, we know that although these are the areas with the worst air pollution, the problem is literally worldwide. On several occasions over the past decade, a heavy cloud of air pollution has covered the entire eastern half of the United States and led to health warnings even in rural areas away from any major concentration of manufacturing and automobile traffic. In fact, the very climate of the entire earth may be affected by air pollution. Some scientists feel that the increasing concentration of carbon dioxide in the air resulting from the burning of fossil fuels(coal and oil) creating a greenhouse effect-holding in heat reflected from the earth and raising the world’s average temperature. If this view is correct and the world’s temperature is raised only a few degrees, much of the polar ice cap will melt and cities such as New York, Boston, Miami, and New Orleans will be under water.

Another view, less widely held, is that increasing particulate matter in the atmosphere is blocking sunlight and lowering the earth’s temperature-a result that would be equally disastrous（灾难的）. A drop of just a few degrees could create something close to a new ice age, and would make agriculture difficult or impossible in many of our top farming areas. At present we do riot know for sure that either of these conditions will happen(though one recent government report prepared by experts in the field concluded that the greenhouse effect is very likely). Perhaps, if we very lucky, the two tendencies will offset each other and the world’s temperature will stay about the same as it is now.

1.As pointed out at the beginning of the passage, people used to think that air pollution ______.

      A．caused widespread damage in the countryside

      B．affected the entire eastern half of the United States

      C．almost brought worldwide effect

      D．existed merely in urban and industrial areas

2.As far as the greenhouse effect is concerned, the author _____________.

      A．shares the same view with the scientists

      B．is uncertain of its occurrence

      C．rejects it as being ungrounded（无根据的）

      D．thinks that it will increasingly destroy the world soon

3.It can be inferred from the passage that                    .

      A．raising the world’s temperature a little would not do much harm to life on the earth

      B．lowering the world’s temperature a little would lead to agricultural disasters

      C．almost no temperature variations have occurred over the past decade

      D．the world’s temperature will remain stable forever

4.This passage is primarily concerned with              .

      A．the greenhouse effect in the world

      B．the measures to adjust the climate

      C．the potential effect of air pollution

      D．the measures to protect the environment