【单选题】

Today we think of automobiles as a necessity, but at first the automobile was a luxury that only the rich could afforD、In 1899, only 600 were built and solD、By 1925, the number approached 20 million. Today you can choose from a huge number of models, some costing 25 times of others. It is said that there are enough motor vehicles in GreatBritain andAmerica to carry their combined population.

Today we can say that much of the world runs on wheels. The four rubber tires of automobile move us from work to play. Wheels spin, and people drive off to their jobs. Tires turn, and they go shopping. Hub-caps whirl, and the whole family goes for a drive in the country.
In addition to automobile, other types of motor vehicles shape our lives. Public buses provide quick and inexpensive transportation. No matter whether you are traveling 500 miles from one city to another, or just going across town, imagine what your life would be like without buses. Trucks also help us in many ways. It is usually cheaper to send goods by truck than by air or train.And because there are many more highways than there are railways, trucks can go to places that trains could not reach. Huge tractor trailers carry goods thousands of miles fromEurope to SaudiArabi
A、Small pick-up trucks help farmers in every country get their produce to market.
The increased use of automobiles has brought a corresponding increase in auto-mobile-related problems such as traffic accidents and traffic congestion. One of the most serious results of our dependence on the automobile is air pollution.Automobiles pump hundreds of pounds of carbon monoxide and other poisonous gases into the air every day. Usually these gases do no immediate damage. However, under certain weather conditions, they may form clouds which cover the skies of large urban areas, threatening the lives of people, especially the sick and the olD、
In the past fifteen years people have become increasingly worried about the effects of air pollution. Therefore, some governments have required automobile manufacturers to find a solution to this problem.As a result, many new cars today have antipollution devices which decrease the amount of pollutants released into the air.
How many types of motor vehicles are mentioned in this passage
A、5 B、4C、9D、6