21、阅读材料，回答21-40题。
There was one thought that air pollution affected only the area immediately around large cities with factories and heavy automobile traffic. At present, we realize 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 east of the United States and brought health warnings in rural areas away from any major concentration of manufacturing and automobile traffic.
In fact, the very climate of the entire earth may be infected by air pollution. Some scientists consider that the increasing concentration of carbon dioxide in the air resulting from the burning of fossil fuels (coal and oil) is creating a "greenhouse effect"-conserving 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 in water.
Another view, less widely held, is that increasing particular matter in the atmosphere is blocking sunlight and lowering the earth's temperature a result that would be equally disastrous. 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 fanning areas. Today we do not know for sure that either of these conditions will happen (though one recent government report drafted by experts in the field concluded that the greenhouse effect is very possible). Perhaps, if we are lucky enough, the two tendencies will offset each other and the world's temperature will stay about the same as it is now.
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 effect on health
D．existed merely in urban and industries areas


22、 As to the greenhouse effect, 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


23、 The word "offset" in the second paragraph could be replaced by __________.
A．slip into
B．make up for
C．set up
D．catch up with


24、 It can be concluded that __________.
A．raising the world's temperature only a few degrees would not do much harm to life on earth
B．lowering the world's temperature merely a few degrees would lead many major fanning 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


25、 This passage is primarily about__________.
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


26、 阅读材料，回答26-45题。
To swim across the English Channel takes at least nine hours. It’s a hard work and it makes you short of breath. To fly over the Channel takes only twenty minutes ( as long as you’re not held up at the airport), but it’s an expensive way to travel. You can travel by hovercraft if you don’t mind the noise, and that takes forty minutes. Otherwise you can go by boat, if you forget your seasickness ills. All these means of transport have their problems and the weary(不耐烦的) traveler often dreams of being able to drive to France in his own car. "Not possible", you say. Well, wait a minute. People are once again considering the idea of a Channel tunnel or bridge.
This time, the Greater London Council is looking into the possibility of building a Channel link straight to London. A bridge would cost far more than a tunnel, but you would be able to goby rail or by car on a bridge, whereas a tunnel would provide a rail link only.
Why is this idea being discussed again? Is Britain becoming more conscious of the need for links with Europe as a result of joining the EEC ( 欧共体) ? Well, perhaps. The main reason, though, is that a tunnel or bridge would reach the twenty square kilometers of London’s disused dockland(船坞地). A link from London to the continent would stimulate trade and revitalize(使...重新有活力) the port, and would make London a main trading centre in Europe. With a link over the Channel, you could buy your fish and chips in England, and be able to eat them in France while they were still warm!
Which of the following statements is TRUE?
A．Swimming across the Channel takes less than four hours.
B．The idea of a Channel tunnel or bridge is a very new one.
C．It is considered to be more difficult to swim across the channel than any other means.
D．A tunnel or bridge would only reach as far as the coast.


27、 A tunnel would be__________
A．less expensive to be built than a bridge
B．more expensive to be built than a bridge
C．less expensive to be built than a rail
D．more expensive to be built than a rail


28、 If they built a Channel tunnel, you would__________
A．neither take a train nor go by car
B．only take a train
C．either take a train or go by car
D．only take a bus


29、 It can be concluded that many of London’s dockyards are__________
A．not used
B．seriously blocked
C．fully used
D．opened again


30、 Channel link would__________
A．allow us to buy fish and chips in France
B．make the journey from Europe to England dangerous but easier and faster
C．decrease more trade for London’s dockyards
D．make London more prosperous again