Read the following paragraph and choose the best topic sentence from the four options that follow.
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.