China has over a billion inhabitants. About 20% live in the towns, the rest of them live in the country. In order to put a stop to enormous increases in population, the Chinese government introduced the one-child policy. People living in towns are forced to have just one child. If they have more children, they are forced to make sacrifices in other areas. For instance they will have to live in a small house and education is no longer free of charge. With twins though this rule does not apply.
The Han Chinese make up about 93% of the population. Furthermore, there are about 55 other minorities, mainly living in the border regions.