单选题

　　 【阅读选择】Today, working less than a 40-hour week, people enjoy more leisure time. Hence, the wise use of leisure time has become an important problem for everyone, young or old. It is a particularly difficult problem for the sick, the aged, and those who have retired from earning a living. Those people have so much leisure that it is hard for them to find interesting and worthwhile ways to use it.

　　 How to spend leisure time wisely is not a particularly difficult problem for people ______.

　　 A、who are very busy everyday

　　 B、who are sick in bed

　　 C、who are aged and in good health　

　　 D、who have retired from work