Why do we think the U.S. is an aging society?

Why do we think the U.S. is an aging society?
【正确答案】:People under 20 years of age made up over a quarter of the US population (27.3%), and people aged 65 and over made up one-eighth (12.8%) in 2009. The national median age was 36.8 years.
【题目解析】:参加教材P185。
掌握“The American Population”知识点。