Enough sleep is important to health.The amount of sleep__56__depends on the age of the person and the conditions in which sleep__57__.The young may need more sleep than the old,but__58__eight hours are enough for the__59__of grown-ups.Some can__60__with less than this amount but__61__may need more.Every person knows his own__62__.It is then a matter of how to__63__it.Sleep should always be__64__to make one relaxed and ready for__65__ work.
Fresh air is__66__to sound sleep.It is not__67__reason for some people to__68__that it is practical to sleep in the open air.__69__a person can keep himself warm,__70__sleeping probably gives the body__71__complete relaxation.
Ability to sleep is largely a__72__.Out-of-door__73__, a good habit of regular. __74__, the avoidance(避免) of late eating, and__75__are all helpful to sound sleep.

