题目内容：

Are you sick of going to bed late and waking up tired? Then grab your hiking boots and a tent．A new study suggests that camping in the great outdoors for a couple of days can reset your body clock and help you get more sleep．

The body clock is an internal system that tells our bodies when it’s time to go to sleep and when it’s time to wake up．Scientists track this clock by measuring the amount of melatonin (褪黑激素) circulating in a person’s blood at any given time．

In a healthy sleeper, melatonin levels rise a few hours before bedtime，stay high through the night，and then settle back down when it’s time to wake up．

In our modem society, however, most of us stay up many hours past sunset and would probably sleep in many hours after sunrise if we could．And the trouble is，your melatonin levels may still be high when your alarm clock goes off in the morning，which leads to fatigue．It may also have other health consequences as well，such as diabetes(糖尿病)，overweight and heart disease．

Professor Kenneth Wright of the University of Colorado in the US wanted to see if our body clocks can be reset by a short stay in nature．His team recruited(招募)fourteen physically active volunteers in their 20s and 30s．Nine went on a weekend camping trip，while the other five stayed home．At the end of the weekend，the researchers reported that in just two days，the campers’ body clocks had shifted so that their melatonin levels began to rise more than an hour earlier than they did before they left on the trip．By contrast，the body clocks of the group that stayed home shifted even later over the course of the weekend．

“This tells us we can reset our clocks fast，”Wright said．

Therefore，if you want to change your sleep patterns you could try to increase your exposure to natural light during the day and decrease the amount of artificial light you see at night．And if that doesn’t work，there’s always camping．

1.What is the author’s main purpose of writing the passage?

A. To explain how a lack of sleep is bad for our health．

B. To inform us of a possible way to adjust the body clock．

C. To analyze how the body clock influences our sleeping habits．

D. To explore how the body clock is connected with melatonin levels．

2.The underlined word “fatigue” in Paragraph 4 probably means“__________”．

A. tiredness    B. excitement

C. refreshment    D. pressure

3.What did Wright’s team discover from their experiment?

A. The body clocks of the two groups didn’t show much difference．

B. The body clocks of those who stayed at home remained the same．

C. Those staying outdoors reset the clock inside their bodies over a short period．

D. Changes to the body clock don’t necessarily affect melatonin levels in our bodies．

4.According to the passage，to change our sleeping habit，we’d better_______．

A. set an alarm clock to wake us up on time in the morning

B. try to reduce melatonin levels as much as possible at night

C. spend several weeks staying in the open air every now and then

D. get exposed to more natural light in the day but less artificial light at night