Studies have shown that a good night's rest helps us stay healthy，both mentally and physically.And researchers say sleep is probably the best tool we have for memory and learning.
   Michael Twery is an expert on the science of sleep and sleep disorders.He told me that a good night's sleep helps to learn better. "Getting a good night's sleep is important for the learning and memory process because it stores the training exercises and the learning exercises into our more permanent（持久的）memory while we' re sleeping 7-8 hours in bed.And then the next morning when you wake up，your mind is better prepared to act on that information."
   But what about getting rest during the middle of the day？Short periods of sleep may help our brains work better or so，says a recent study on napping.
   Past studies have shown that napping can help babies and young children learn better.And napping can help brain performance in older adults.Taking a nap may also help this group of people fight off age-related memory loss.
   Researchers recently looked at information provided by nearly 3，000 Chinese adults，aged 65 years or older.They wanted to learn if napping after a mid-day meal had any effect on the mental performance of the subjects.Nearly 60 percent of those 3，000 people said they did take a nap after lunch and that their naps lasted anywhere from 30 to 90 minutes.Most of the subjects said they napped for about an hour.
   The study found that people who took an hour-long nap did much better on mental tests than those who did not nap.The hour-long nappers also did better on the tests than those who napped for shorter and longer periods.
   Keep in mind，however，that these are the findings for those over the age of 65.Yet Doctor Michael Twery notes that an hour long nap may be too long for young，healthy adults. "Currently，we're recommending that we try to sleep for about 30 minutes or less.And 30 minutes is enough to remove the pressure to sleep and will help us feel more awake.If we nap longer，we will get trapped into those deeper layers of sleep，which can be hard to get out of."

（1）According to Twery，why does a good night's sleep help to learn better？

D

D

A．Because it helps to remember clearly.
B．Because it helps to think deeply.
C．Because it can help act quickly.
D．Because it helps to remember longer and act more effectively.
（2）What's the meaning of nap？

B

B

A．A long time sleep during daytime.
B．A short time sleep during daytime.
C．A short time sleep during the night.
D．A long time sleep during the night.
（3）What kind of people does nap help？

D

D

A．Students.
B．Babies.
C．Old people.
D．Babies，young children and the old.
（4）What may help old people decrease memory loss because of age？

C

C

A．8 hours' night's sleep.
B．A good night's sleep.
C．Napping during the middle of the day.
D．Long time sleep during the middle of the day.
（5）According to the passage，which of the following statements is true？

D

D

A．Deeper layers of sleep is good for young people's study and work.
B．Young healthy adults need an hour nap.
C．30 minutes is too short for young people to remove the pressure to sleep.
D．A good night's rest helps us stay healthy，both mentally and physically.