填空题

People who live in heavily industrialized areas do not get as much sunlight as they should. Dust (1) over a city at altitudes (海拔) of between 4,000 and 8,000 feet cuts out between 20 and 50 percent of the sunlight and up to 90 percent of the ultraviolet light (紫外线). But dust is not the only thing to (2) about. When fuels are burned, whether in a factory, or in a home, or in the engine of a car, CO₂ is given off. CO₂ in the atmosphere acts as a kind of (3) around the earth, keeping warms in and so slowly raising the (4) of the earth. This could really change the climate all over the world.
Everybody wants to have a car. (5) , while they are giving us so much pleasure, cars are also poisoning us. The amount of dangerous substances sent out by a car is quite (6) . Did you know, for example, that a hundred cars produce on (7) a third of a ton of CO₂ as well as many other (8) substances every day
Now, more and more people are realizing the importance of clean air. Schools are now teaching about the pollution problems. Scientists and engineers are trying to (9) new engines for cars. But what about the millions of cars already in use Must they all be thrown away It might be very (10) to change them so that they, too, are pollution-free.
A. forge B. screen C. expensive D. floating
E. unfortunately F. average G. poisonous H. develop
I. temperature J. surprising K. overtaking L. essential
M. regulation N. generously O. worry