单项选择题
（）is not installed on the emergency switchboard.
A.Ammeter and changeover switch B.Speed governor device C.Synchroscope D.Wattmeter
单项选择题 （）is not installed on the emergency switchboard.
单项选择题 （）can be used to prevent hydraulic system overloaded or keep the pressure of oil outlet from pump constant.
单项选择题 The symbol (GB786√1-93) at right side represents （）
