单项选择题
Prior to any overhaul work on electric equipment, it is important to ensure the circuits are （）.
A.live B.dead C.excited D.on line
单项选择题 （） control system is one in which the control action is independent of the output.
单项选择题 （） power is the power developed within the cylinder and can be measured by an engine indicator.
单项选择题 The operating medium for control systems may be （）.
