The magnetic field is provided by electromagnets so arranged that adjacent poles have ___.
A.opposite polarity
B.the same polarity
C.negative polarity
D.positive polarity

单项选择题The division of kilowatt load between two paralleled alternators is determined by theA.amount of field excitation of the leading machineB.load-speed characteristics of the governorsC.amount of field excitation to the lagging machineD.type of alternator

单项选择题Some refrigeration systems have chemical moisture indicators installed in conjunction with the sight glass in the liquid line If excess moisture is present in the system, the indicator willA.activate the driersB.change colorC.secure the compressorD.add a predetermined amount of liquid drier