题目内容：
阅读短文，回答题A pioneering study by Donald Appleyard made the surprising discovery that a sudden increase in the volume of traffic through an area affects people in the way that a sudden increase in crime does. Appleyard observed this by finding three blocks of houses in San Francisco that looked much alike and had the same kind of middle -class and working -class residents, with approximately the same ethnic mix. The difference was that only 2,000 cars a day ran down Octavia Street (LIGHT street, in Appleyard’s terminology) while Gough Street (MEDIUM street) was used by 8,000 cars a day, and Franklin Street (HEAVY street) had around 16,000 cars a day. Franklin Street often had as many cars in an hour as Octavia Street had in a day.
Heavy traffic brought with it danger, noise, fumes, and soot, directly, and trash secondarily. That is, the cars didn’t bring in much trash, but when trash accumulated, residents seldom picked it up. The car, Appleyard determined, reduced the amount of territory residents felt responsible for. Noise was a constant intrusion into their homes. Many Franklin Street residents covered their doors and windows and spent most of their time in the rear of their houses. Most families with children had already left.
Conditions on Octavia Street were much different. Residents picked up trash. They sat on their front steps and chatted with neighbors. They had three times as many friends and twice as many acquaintances as the people on Franklin.
On Gough Street, residents said that the old feeling of community was disappearing as traffic increased; People were becoming more and more preoccupied with their own lives. A number of families had recently moved. And more were considering it. Those who were staying expressed deep regret at the destruction of their community.
Appleyard’s study focuses on the influence of . A．traffic volume on the residents
B．social classes on the transportation
C．rate of crime on the neighborhood
D．degree of pollution on the environment
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