Most people today think of sleep as one continuous period of downtime．This is not the way people used to sleep．According to researchers，in earlier times，people divided sleep by first sleeping a few hours，waking up，then going back to sleep．In the first period，you would typically sleep until midnight or shortly afterwards．Halfway through the night，you came out of first sleep，you would stay in bed and relax quietly．It was called the watching period．Then you would start to feel sleepy．so would return to bed and tall asleep again for your second sleep．This period would continue until early morning when daylight arrived．With no artificial lighting in homes，people naturally woke up early to take advantage of sunlight．
Before the 18th century, people had no gas or electricity in their homes．Fire，candles，or oil lamps were the common forms of lighting．This lack of artificial lighting in homes contributed to people’s sleep patterns．It made sense for people to go to bed early．
Today，human may consider divided sleep a strange habit，but sleep researchers say that it is actually a more natural sleep pattern．Dr．Thomas Wehr of the U．S．National Institute of Mental Health has studied human sleep．He thinks that modern sleep problems occur because the older, natural way of sleep is breaking through the more recent continuous sleep pattern．Wehr and other scientists believe that artificial lighting has altered the way people sleep．In a research study，he asked 15 adults to rest and sleep in darkness for 14 hours(from 6：00 P．M．to 8：00 A．M．)．At first，the subjects took a few hours to get to sleep，and then slept 11 hours a night．Then overtime，they switched to divided sleep．They fell asleep for about three to five hours in the evening，stay awake for an hour or two，and then slept again for four hours till early morning．
We modern humans generally do not practice divided sleep．However, many of us have the experience of waking up in the middle of the night．We usually consider this a sleeping“problem”．but perhaps we should look at it as natural behavior．Divided sleep may be the way we should all be sleeping．A first sleep followed by a relaxation period and a second period of sleep could help all of us to beat the stress of our fast-paced lives．
According to the first paragraph，we know the people in the past ____________．

A．did not sleep as well as people today

B．divided their sleep into two parts

C．woke up and went out during the night

D．fell asleep easily because of hard work

In Paragraph 3，what does the research study suggest?

A．Divided sleep is a strange way to sleep．

B．Divided sleep means sleeping 11 hours in one period．

C．Divided sleep is a natural sleep pattern for humans．

D．Divided sleep occurs when people sleep with artificial lights．

Which of the following is NOT true according to the text?

A．People had a divided sleep pattern only in the 18th century．

B．It may be natural to wake up in the middle of the night．

C．Scientists agree that artificial lighting has changed the way people sleep．

D．Some of the people today are not familiar with the practice of divided sleep．

What conclusion does the author make about divided sleep?

A．It is one type of sleeping problems．

B．It is not the best sleep pattern for everyone．

C．It shouldn’t be accepted by modern humans．

D．It could be helpful for people to handle daily stress．