有一种液面微变监视器，基本结构原理如图所示，光束发射器始终以一定角度向被监视的液面发射一束细光；光束经液面反射，其反射光被水平放置的平面光电转换接收器接收，再通过显示器显示出来，反射到光电转换接收器的光点由S
移向S
，则表明被监视的液面 ；若接收器上接收到的光点由S
移到S
，则说明被监视的液面 （填“上升”或“下降”）。
上升 下降
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| Mobile phones are everywhere in big cities. It seems that 1 can survive without one. Mobile phones are a great 2 to stay connected with friends and family. 3 , it is important to remember that there are certain times 4 you should not be using your phone, especially as a student, during school. 5 you are in class, you should not be sending your friends text messages 6 taking phone calls. Your classmates and teacher should not have to deal with this rude 7 . Aren't you at school to learn? In the United States, students would never be allowed to 8 their mobile phones during class. If you were to send or 9 a text message you would probably be kicked out of class. It is very 10 to hear a lot of tones and ringing during 11 . There are many more rules for mobile phone use in America and it is to 12 respect for those around you. As a teacher in China, I have to 13 students using mobile phones every day. I have told my class to 14 their phones, but many students do not listen. The 15 to be connected all the time seems to be more 16 than the desire to learn. It's easy to understand 17 it is so tempting (诱惑人的) to have your phone on during class. It seems so easy just to send a short text message; it's not hurting anyone, is it? But you may actually be hurting 18 when you do this. Your teacher knows when you use your phone and may give you a 19 grade. Sending a text message also takes your attention away from what's going on in class, you may 20 something important. | ||||
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