One day, a teacher was giving a speech to his students .He held up（举起）a glass of water and asked the class. "How heavy do you think this glass of water is ?"
The students’ answers ranged（范围） from 20g to 500g .
"It does not matter on the weight itself .It depends on how long you hold it .If I hold it for a minute ,it is OK. If I hold it for an hour ,I will have an ache in my right arm .If I hold it for a day ,you will have to call an ambulance（救护车）.It is exactly the same weight ,but the longer I hold it ,the heavier it becomes."
"If we carry our burdens （负担）all the time, sooner or later ,we will not be able to carry on ,the burden becoming increasingly heavier ."
"What you have to do is to put the glass down ,rest for a while before holding it up again ."
We have to put down the burden sometimes ,so that we can be refreshed and are able to carry on .
So before you return home from work tonight ,put the burden of work down .Don’t carry it back home. You can pick it up tomorrow .
Whatever burdens you are having now on your shoulders, let it down for a moment if you can .
The teacher brought a glass of water to the class because ______
A. he was very thirsty  B. his arms were strong  C. it was a good example
"A glass of water " in this passage referred to （指）______
A. knowledge  B. the burden  C .the time
Accordign to the teacher ,you may feel ______if you put down the burden sometimes.
A. more energetic  B. much heavier  C. more stressed out （压力、紧张）
This was a lesson about______
A. how to relax oneself in life  B. how to solve a physics problem .
C. how to keep fit by drinking water
Which of the following statements is TRUE according to the passage ?
A .You could become heavier and heavier if you held a glass of water in your hand .
B. All the students in the class knew what the weight of the glass of water exactly was
C. The teacher had a good way of making his lesson clear and easy to be understood