单项选择题
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
单项选择题 CFC refrigerants exposed to high temperature or direct flame, will decompose and may produce（）
单项选择题 The major difference between the discharge and suction valves installed in most low pressure, reciprocating air compressors is that（）
单项选择题 Which of the following problems will occur if the internal drain at either end of a hydraulic, two-way, spool-type directional control valve cylinder were to become plugged?（）