Biological Clock
When the sun rises on a warm and sunny day, you can see some flowers open up. When they close late in the afternoon, other flowers open.
Biological rhythms（生物节律）, like the opening and closing of flowers, happen all over nature. But not all of them are daily rhythms. Some, like the beating of our heart , happen every second. ___1___
Scientists use the term biological clock to describe the timing that controls biological rhythms. ___2____ In some animals it is probably controlled by the brain. In plants and other living things that have no brain, it must be something else.
The migration of animals happens when a signal is sent out. For example, when days become shorter, birds leave the northern parts of the world and fly south where it is warm. ____3___
Humans also have biological clocks that control their daily rhythms. When people travel by plane from one continent to another, they often cross many time zones. Their internal clocks don’t seem to work correctly. We call this jet lag（时差）.
___4____ People who work night shifts also have problems with their biological clocks. They may not be as active as people who work during the daytime.
Biological clocks control many rhythms of life. ___5____ Doctors are looking for new ways to make travelling more comfortable and medical treatment more effective .
选项
A.But where can you find it?
B.This makes them feel tired.
C.In the summer they fly back to have babies.
D.We are learning more and more about them.
E.Biological clocks can be adjusted.
F.Other rhythms are based on months, seasons or years.
【正确答案】：F A C B D
【题目解析】：1. 根据1空前一句“But not all of them are daily rhythms. Some, like the beating of our heart , happen every second.”关键词“daily rhythms”“happen every second”可知下一句谈论的是生物节律发生的其他类型频次。
2. 根据2空后一句“In some animals it is probably controlled by the brain.”可知前文谈论的是生物节律在哪里发生。
3. 根据3空前文“For example, when days become shorter, birds leave the northern parts of the world and fly south where it is warm.”可知后文要提到季节变换鸟类的生活习性。
4. 前文“We call this jet lag（时差）.”可知倒时差时人会较疲惫。
5. 空前为“Biological clocks control many rhythms of life.”生物钟控制着很多生命的节律，空后为“Doctors are looking for new ways to make travelling more comfortable and medical treatment more effective .”医生正在寻找一些新的办法，让我们的旅途更加舒适，让药物治疗更加有效。我们对节律的了解越来越多。（因为对它了解越来越多，才会找到更好的方法）
