阅读理解。阅读下列短文, 从给的四个选项 (A、B、C和D) 中, 选出最佳选项。
America is growing older. Fifty years ago, only 4 out of every 100 people in the United States were 65 or older. Today, 10 out of every 100 Americans are over 65. The aging of the population will affect American society in many ways — education, medicine, and business. Quietly, the aging of America has made us a very different society — one in which people have a quite different idea of what kind of behavior is suitable at various ages.
