先看一个关于circadian rhythm的介绍。有两个要点。一个是每人都会有自己的alert time 和tired time。 第二个要点就是这个rhythm随着时间推移可能会改变。那个lecture里面教授就举了2个例子。首先说在大学的时候他习惯晚上学习，因为那个时候他精神好，效率高，睡的比别人都晚。早上就会特别困，起不来，所以他从来不选早上的课。第二个例子说他做了年纪大了做了教授发现，早上效率比较高，晚上就各种累。所以现在他的习惯颠倒了。早上看看书，备课，晚上就早早睡觉了。
The material describes circadian rhythm. There are two characteristics. First of all, everyone has acquired their respective alert time and tire time, but secondly, the rhythm is to change with the time going by. The professor talked about two examples. When he was in college, he was used to learning during the night, because he thought he had high efficiency at night and thus went to sleep later than others. But at the same time, he was quite sleepy during the morning due to lack of sleep. However, after he became professor in the university, he realized that the most efficient period has shifted to morning when he could better focus. But at night, he was quite tired. Therefore, he has changed his habit and started to deal with reading and course preparation in the morning. (136 words)
