Do you know how much your children sleep?
According to the National Sleep Foundation,        should sleep twelve to eighteen hours        of every twenty-four. With a gradual         to twelve to fourteen hours for toddlers(初学走路的孩子) one to three; eleven to thirteen hours for         three to five; and ten to eleven hours for schoolchildren         five to ten.
But things get really       at adolescence. Not only do teenagers need more sleep than     __---eight and a half to nine and a quarter hours a night, according to the sleep foundation - but the times           which they get sleepy and are able to awaken          and feel rested shift in a        that does not match to the        times at most schools.
Sleep studies have shown that the typical teenager does not fall asleep readily before 11 p. m. or later.        many have to get up by 6 a. m. or          to get to school for a class          starts at 7:30 or 8 a.m. More than a few         off during that class, and often the          one as well. Even if awake, they're in no condition to learn much of anything.
In one study, more than 90 percent of teenagers         they slept less than the           nine hours a night, and 10 percent said they slept less than six hours.
      _ James B. Maas, a Cornell University psychologist and Leading sleep researcher, has observed, most teenagers are "walking zombies(僵尸)"         they get far too little sleep.

A．children B．newborns C．elders D．youngsters

A．from B．with C．out D．up

A．reduction B．increase C．growth D．improvement

A．teenagers B．students C．babies D．preschoolers

A．related B．separated C．aged D．varied

A．demanding B．challenging C．satisfying D．encouraging

A．adults B．toddlers C．babies D．schoolchildren

A．in B．on C．at D．for

A．excitedly B．early C．casually D．naturally

A．form B．means C．method D．way

A．end B．start C．holiday D．examination

A．Since B．For C．Yet D．Then

A．nicer B．earlier C．cleaner D．better

A．that B．its C．what D．whose

A．put B．take C．doze D．cut

A．next B．other C．last D．new

A．examined B．surveyed C．reported D．convinced

A．regulated B．recommended C．analyzed D．reported

A．Like B．Since C．As D．Furthermore

A．because B．which C．while D．still