问题
单项选择题
机床运转出现的异常现象中，常见于各种机床所使用的电动机及轴承齿轮箱的是( )。
A．转速异常
B．温升异常
C．振动和噪声过大
D．出现撞击声
答案
参考答案：B
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机床运转出现的异常现象中，常见于各种机床所使用的电动机及轴承齿轮箱的是( )。
A．转速异常
B．温升异常
C．振动和噪声过大
D．出现撞击声
参考答案：B
People talk with words. Do you think you can talk without words? A smile on your face __ that you are happy and friendly. Tears in your eyes tell __ that you are sad. When you __ your hand in class, the teacher knows you want to say __ or ask questions. You shake your head, and people know you are saying “ no”. You nod and people know you are saying __. Other things can also give some __. For example, a sign at the bus stop helps you to know which bus to take. A sign on the wall of your school helps you find the library. Signs on doors tell you __ to go. People talk to each other in many other __. An artist uses his pictures to tell about the blue sea, about beautiful mountains and many other things. __ write books to tell you about all wonderful things in the world and also about people and their ideas. They all help us to know __ is going on in the world.
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