D
Everyone has those nights-you lie in your bed for hours, tossing and turning, totally unable to fall asleep. You wish you could just turn your brain off as if it were a light. That would make things much easier, wouldn’t it?
Now it looks like you are one step closer to this wild dream of yours-scientists from Oxford University, UK have just discovered the “switch” that tells the brain to go to sleep, reported Forbes.
To understand the study, you first need to know that there are two mechanisms(机能) that regulate sleep. There’s one that we’re already familiar with —our body clock, which works in a 24-hour cycle based on the light changes throughout the day.
The other one is what scientists call the sleep “homeostat(动态平衡系统)”. This mechanism has nothing to do with daylight. Instead, it keeps track of the brain’s waking hours and urges it to rest if it has been awake for a long time. “It is similar to the thermostat(自动调温器) in your home. A thermostat measures temperature and switches on the heating if it’s too cold,” Professor Gero Miesenbock, who led the study, told The Telegraph.
Our bodies use both of the mechanisms to regulate sleep. “The body clock says it’s the right time, and the sleep thermostat has built up pressure during a long waking day,” explained Miesenbock.
There is no way that scientists can trick the body clock. But with the sleep homeostat, there might be something they can do.
The researchers found that the sleep homeostat works by activating a specific group of nerve cells, or neurons, in the brain. They tested their theory on fruit flies by removing the neurons from the insects’ brains. And as expected, they found that the flies without the homeostat neurons did not keep a regular sleep pattern anymore.
Now that scientists have pinpointed the exact place in the brain— or, the “switch”—that regulates sleep, they can begin investigating how to activate these cells at any given time so that people can be sent to sleep instantly.
More importantly, figuring out how sleep mechanisms work may also help us to one day unravel one of the oldest mysteries of all: why do we need to sleep in the first place?
What is the article mainly about?

A．A new way to treat sleep disorders.

B．The discovery of the sleep “homeostat”

C．Advice on what to do when you fail to fall asleep.

D．A comparison of the two mechanisms that regulate sleep.

How does the author explain the function of the sleep homeostat?

A．Through examples.

B．With comparisons.

C．Through cause and effect analysis.

D．By presenting research findings.

What can we conclude from the article?

A．Generally, the sleep homeostat has less effect on people during the day than at night.

B．There is little scientists can do to affect the way the sleep homeostat works.

C．What makes us go to sleep at night is probably a combination of the two mechanisms.

D．The more homeostat neurons there are in one’s brain, the more easily one can fall asleep.

The underlined word “unravel” in the last paragraph is closest in meaning to        .

A．put up with	B．figure out
C．keep track of	D．take notice of