When tires are burned at the energy plants____________

Câu hỏi: Read the following passage and mark the letter A, B, C or D on your answer sheet to indicate the correct answer for each of the questions from 35 to 42.
Around the world, billions of tires from trucks and cars are replaced every year. In the United States, about 260 million used truck and auto tires are thrown away every year. Where do the old tires go? Quite often, they go into large dumps where they remain for many years.
The mountains of worn- out tires in these dumps present a number of health and environmental dangers. First, thet attract mosquitoes and rats, which then spread disease among humans. The tires can also catch on fire, and these fires are very difficult to put out. They may burn from a few days to a few months. While the tires burn, they release cancer- causing gases into the air. These gases spread over nearby towns and cause health problems for people who live there.
After a tire dumps fire is put out, pieces of burned tires remain on the ground. When it rains, chemicals from the burned parts wash into the soil and into the ground water. This pollutes the soil and the drinking water in the area.
Aside from these problems, the tire dumps represent a terrible waste of resources. So, in order to avoid the problems and the waste, people are looking for ways to reuse or recycle tires. Recycling is common for other materials, such as paper, glass, and aluminum. Now tires are also being recycled in a number of creative ways.
One solution is to burn the tires to create energy. An energy company with plants in Connecticut and California burns tires to produce steam for generating electricity.
When the tires are burned properly, the fire does not pollute the air. Every day,'workers check to make sure that no dangerous gases are allowed out of the energy plant's chimneys. A total of about 15 million tires are burned every year in the company's two plants. This produces enough electricity to supply about 42,000 houses.
Another solution is to find a new use for the tires. Tires are now being used to make various products, from doormats to fishing supplies. Several shoes companies have started using tires to make the soles of tennis shoes. This is not a new idea, in fact. During the Great Depression, shoes with tire soles were very common in the United States.
The state of Maine has found yet another use for old tires. The climate in Maine is very cold, and in the winter the ground freezes solid. Large bumps are formed in the roads and then in the spring, the bumps may turn into holes. Roads must be rebuilt often, at great expense to the state. To prevent this, road workers have started to use old tires broken into small pieces and spread in a thick layer underneath the surface of a new road. The tires then act as a blanket, keeping the ground below the road from freezing. This way the road surface remains smooth.
Up to now, only a small percentage of used tires are being recycled in the United States. But there are plans and new ideas about ways to reuse more of the tires that end up in tire dumps.
When tires are burned at the energy plants____________
A. air pollution is a big problem.
B. air pollution is not a problem.
C. only a few fires are burned.
D. workers are exposed to dangerous gases.