单项选择题
The greatest detrimental effect on idle electrical equipment, such as cargo pump motors, is the（）.
A.loss of residual magnetism B.absorption of moisture in the insulation C.insulation varnish flaking D.dirt collecting on the windings
单项选择题 The Wheat-stone bridge is a precision measuring instrument utilizing the principle of changes in（）.
单项选择题 Which of the motors for the devices listed below is fitted with an instantaneous overload relay?（）
单项选择题 One factor that determines the frequency of an alternator is the（）.
