单项选择题
In a three-phase circuit, the phase voltages are （）
A.120°apart B.160°apart C.180°apart D.360°apart
单项选择题 The frequency of an alternator at a given RPM is determined by the （）.
单项选择题 The pushbutton on the handset of a ships sound-powered telephone must be depressed to （）.
单项选择题 Which of the following statements is true concerning simple parallel resistance circuits?（）
