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.

    Youth sport has the potential to accomplish three important objectives in children's development. First, sport programs can provide youth with opportunities to be physically active, which can lead to improved physical health. Second, youth sport programs have long been considered important to youth's psychosocial development, providing opportunities to learn important life skills such as cooperation, discipline, leadership, and self-control. Third, youth sport programs are critical for the learning of motor skills; these motor skills serve as a foundation for future national sport stars and recreational adult sport participants. When coachers develop activities for youth practices and when sport organizations design youth-sport programs, they must consider the implication of deliberate play and deliberate practice.

Research from Telama （2006） states that regular participation in deliberate play or deliberate practice activities during childhood and youth （ages nine to eighteen） increases the likelihood of participation in sports during adulthood by six times for both males and females. Côté （2002） defines deliberate play activities in sport as those designed to maximize enjoyment. These activities are regulated by flexible rules adapted from standardized sport rules and are set up by the children or by an involved adult. Children typically change rules to find a point where their game is similar to the actual sport but still allows for play at their level. For example, children may change soccer and basketball rules to suit their needs and environment （e.g. in the street. on a playing field or in someone's backyard）. When involved in deliberate play activities, children are less concerned with the outcome of their outcome of their behavior. （whether they win or lose） than with the behavior. （having fun）.

    On the other hand, Ericsson （1993） suggests that the most effective learning occurs through involvement in highly structured activities defined as deliberate practice. Deliberate practice activities require effort, produce no immediate rewards, and are motivated by the goal of improving performance rather than the goal of enjoyment. When individuals are involved in deliberate play, they experiment with different combinations of behaviors, but not necessarily in the most effective way to improve performance. In contrast, when individuals are involved in deliberate practice, they exhibit behavior. focused on improving performance by the most effective means available. For example, the backhand skills in tennis could be learned and improved over time by playing matches or by creating fun practice situations. However, players could more effectively improve their backhand performance by practicing drills that might be considered less enjoyable. Although drills are used in most effective means available practice might not be the most enjoyable, they might be the most relevant to improving performance.

    （Note: Answer the questions or complete the statements in NO MORE THAN TEN WORDS）

一份数学试卷，只有25个选择题，做对一题得4分，做错一题倒扣1分，某同学做了全部试卷，得了70分，他一共做对了（　　）