C. It provides a free download service through the app for digital recipes.

　　D. It doesn't accept new restaurants unless recommended by trusted chefs.

　　2. What can we learn about the app from the last three paragraphs?

　　A. It is the idea that was created by two famous chefs.

　　B. It has enabled foodies to eat with their favorite chefs.

　　C. Developers spent a lot of time and energy building it.

　　D. Most of its material comes from travel guidebooks.

　　B

　　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 modern 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.

　　3. The underlined word "fatigue" in Paragraph 4 probably means _

A. excitement