理工类辅导资料：阅读理解Making Light
All we have a clock located inside our brains. Similar to your bedside alarm clock， your internal clock2 runs on a 24-hour cycle. This cycle，called a circadian rhythm，helps control when you wake，when you eat and when you sleep.
Somewhere around puberty，something happens in the timing of the biological clock. The clock pushes forward，so adolescents and teenagers are unable to fall asleep as early as they used to. When your mother tells you its time for bed，your body may be pushing you to stay up3 for several hours more. And the light coming from your computer screen or TV could be pushing you to stay up even later.
This shift4 is natural for teenagers. But staying up very late and sleeping late can get your bodys clock out of sync with the cycle of light and dark5. It can also make it hard to get out of bed in the morning and may bring other problems，too. Teenagers are put in a kind of a gray cloud6 when they dont get enough sleep，says Mary Carskadon，a sleep researcher at Brown University in Providence，RI7 .It affects their mood and their ability to think and learn.
But just like your alarm clock，your internal clock can be reset. In fact，it automatically resets itself every day. How? By using the light it gets through your eyes.
Scientists have known for a long time that the light of day and the dark of night play important roles in setting our internal clocks. For years，researchers thought that the signals that synchronize the bodys clock8 were handled through the same pathways that we use to see.
But recent discoveries show that the human eye has two separate light-sensing systems. One system allows us to see. The second system tells our body whether its day or night.
词汇：
circadian adj. 昼夜节奏的，生理节奏的
adolescent n.青少年；adj.青少年的
puberty n.发育；青春期
sync n. (口语)同步；和谐，协调
synchronize V.(使)同时发生；(使)同步
注释：
1.make light of ：轻视，不在乎。例如： We should not make light of their achievements.我们不应当低估他们的成就。
2. your internal clock ：指的是第一句中的a clock located inside our brains ，也即是第二段第一句中的the biological clock (生物钟)。
3. stay up：不睡觉，熬夜
4. This shift：这种调整。指上文所描述的由于生理时间的变化青少年上床时间越来越晚的现象。
5. get your bodys clock out of sync with the cycle of light and dark ：打乱了你的生物钟与昼夜时间循环之间的平衡
6. gray cloud ：提不起精神的状态
7. Brown University in Providence， RI：位于美国罗得岛州普罗维登斯的布朗大学。RI是Rhode Island(罗得岛)的首字母缩写；Providence 是罗得岛州的首府。布朗大学是美国一流大学，
创建于1764 年，是世界闻名的美国"常春藤联盟"(还包括哈佛大学、耶鲁大学、普林斯顿大学、布朗大学、哥伦比亚大学、宾夕法尼亚大学、达特茅斯大学和康奈尔大学)中的一员。
8. the signals that synchronize the bodys clock：平衡生物钟的光信号