Read the following paragraph and choose the best topic sentence

Read the following paragraph and choose the best topic sentence from the four options that follow. Write the corresponding letter of your choice in the blank provided. 　Most adults sleep between seven and nine hours，but occasionally people turn up who need twelve hours or so，while some rare types can get by on three or four. Rarest of all are those legendary types who require almost no sleep at all; respected researchers have recently studied three such people. One of them—a healthy，happy woman in her seventies—sleeps about an hour every two or three days. The other two are men in early middle age，who get by on a few minutes a night. One of them complains about the daily fifteen minutes or so he’s forced to “waste” in sleeping. [A] Sleep is a waste of time. [B] Adequate sleeping hours are essential for most adults. [C] Adults and teenagers vary widely in their sleeping habits. [D] A fact about sleep is that individual needs for it vary widely. Your choice:__________
【正确答案】：D
【题目解析】：本类题型考察的是主题句和推展句之间的关系。主题句是推展句的概括和总结，推展句是主题句的解释和说明。根据这一关系，我们可以通过对推展句的阅读，来确定某个段落的主题句。本段中的推展句都是说的不同的人不同的睡眠时间，也就是说，睡眠时间的长短是因人而异的，所以我们选定D句为本段主题句。