单项选择题

Operational amplifiers, used primarily in analog circuits, are characterized by（）

A.high input impedance, high gain and low output impedance
B.high input impedance, high gain and high output impedance
C.low input impedance, low gain and high output impedance
D.low input impedance, high gain and low output impedance

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CFC refrigerants exposed to high temperature or direct flame, will decompose and may produce（）

A.methyl chloride
B.ammonia
C.hydrofluoric acid
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单项选择题

The major difference between the discharge and suction valves installed in most low pressure, reciprocating air compressors is that（）

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单项选择题

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B.The valve would be placed in hydraulic lock
C.The spring loaded relief ports would open
D.The buffering chambers would be unable to function