高考英语阅读练习——科普环保类

高考英语阅读训练——科普环保类 （一） It is 7 am and the alarm is going off. You know you have to be out of bed to catch the bus. But the urge to bury yourself in the bed is ever so strong. Sounds familiar? Why is it that teens find it difficult to get themselves out of bed in time every morning or stay sharp and focused during the first couple of hours of school? During adolescence, the body goes through many changes and these include a shift in sleep patterns. Researchers from MIT have been tracking the body’s need for sleep in teenagers. They found that though adolescents need as much as 9.5 hours of sleep a day, they get to bed later and later with each passing year. In fact, the sleep cycle shifts later by as much as 12 to 18 minutes each year between the ages of 10 and 20! So by the time a 10​year​old who sleeps at 8 pm grows to be 17 or 18, his body naturally wants to stay up till 10：30 pm or 11 pm. According to researchers, this is because of a hormone called melatonin (褪黑激素) that is secreted (分