根据下面资料，回答
Today, people all over the world are moving out of small villages in the country to go and live in big, noisy cities. They are moving from the peaceful hills, mountains, fields, rivers and streams of the countryside to the busy world of streets, buildings, traffic and crowds. This movement from rural areas to urban areas has been going on for over two hundred years.
In many countries, the main reason why people come to live in towns and cities is work. After one or two large factories have been built in or near a town, people come to find work, and soon an industrial area begins to grow. There is usually a residential area nearby, where the factory workers can live. The families of these workers need schools, hospitals and shops, so more people come to live in the area to provide these services and a city grows.
In every major city in the world, there is a business district where the big companies have their main offices. In the United States, this area is usually in the city centre. It is here that you can see the huge skyscraper office blocks. The people who work here often travel a long way to work each day. Many of them live in the suburbs of the city, far away from the industrial area and the city centre. Some suburbs are very pleasant, with nice houses and big gardens. There are usually parks for children to play in and large department stores where you can buy all you need.
But what is the future of the big cities? Will they continue to get bigger? Perhaps not. Some major cities have actually become smaller in the last ten years, and it is quite possible that one day we will see people moving out of the major cities and back into smaller towns and villages.
Why do people move to live in cities or towns?

A.Because they can live more comfortably there.
B.Because they prefer a noisy life to a peaceful life.
C.Because they want to find work.
D.Because they are sure of having a better life there.