[简答题]尽管人为什么要睡觉这一头号题我们尚未弄清楚，但毫无疑问，人需要睡觉，其他动物也是如此。醒与睡的交替模式是与我们的习惯和感官密切相关的。动物靠视力寻找食物、栖息地和庇护，它们与人一样白天的大部分时间活动，晚上睡觉。为保持身体健康，一个人所需的睡眠时间因年龄不同而大不相同。学龄前儿童通常需要10～12个小时的睡眠时间，中小学生9～11个小时，成年人7～9个小时。成年人随着日益变老所需睡眠时间似乎也逐渐减少。睡眠时间也随种族不同而不同。据说，日本人，包括儿童和成年人，睡眠时间比欧洲人少。但这种不同也许是由于生活习惯而不是由于种族的原因造成的。

参考答案: Although we are not sure why we sleep, there is no doubt that we need to do so and so do most other animals. The pattern of sleep and wakefulness is closely connected with our habits and senses. Animals which depend on sight for food, shelter and defense, like man, are for the most part are active during the day and asleep at night. The amount of sleep needed by a person to remain in full health varies considerably with age. Preschool children generally need ten to twelve hours’ sleep, schoolchildren nine to eleven hours and adults seven to nine hours. Adults seem to need progressively less sleep as they grow older. The amount of sleep also varies with races. It has been said that the Japanese, both children and adults, sleep less than Europeans, but that may be due to habit rather than race.