单项选择题
A．the United Nations thinks it possible to avoid a population explosion B．5.1 billion people are living in the underdeveloped countries C．in advanced nations the population growth is being controlled D．the world's population is increasin
A．100 B．115 C．130 D．145
A．a lot of social problems B．medical advances C．a decrease in food production D．a worse life in every nation with 3 billion