单项选择题
Sacrificial zinc anodes are used on the saltwater side of diesel engine heat exchangers to（）.
A.reduce electrolytic action on heat exchanger metals B.keep heat transfer surfaces shiny and clean C.prevent rapid accumulation of marine growth D.provide a protective coating on heat exchanger surfaces
单项选择题 With a （） load the voltage and current are in phase.
单项选择题 The star-delta starter is an effective method of （） voltage starting of a motor.
单项选择题 The （）, cage rotor induction motor is the first choice marine motor in most modern ships because of its electrical and mechanical simplicity.
