单项选择题
An electrical device which prevents an action from occurring until all other required conditions are met is called a/an （）.
A.limit B.monitor C.modulator D.interlock
单项选择题 The frequency output of an operating alternator is controlled by the （）.
单项选择题 The greatest detrimental effect on idle electrical equipment, such as cargo pump motors, is the（）.
单项选择题 The Wheat-stone bridge is a precision measuring instrument utilizing the principle of changes in（）.
