单项选择题

Which of the following electric motors would be the safest and most reliable to use on the main deck of a vessel in foul weather conditions?（）

A.Sealed motors
B.Drip proof motors
C.Enclosed motors
D.Watertight motors

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单项选择题

A resistance in a circuit of unknown value is to be tested using the voltmeter/ammeter methodTherefore, the meters should be connected with（）.

A.both meters in series with the resistance
B.both meters in parallel with the resistance
C.the ammeter in series and the voltmeter in parallel with the resistance
D.the ammeter in parallel and the voltmeter in series with the resistance

单项选择题

An accidental path of low resistance, allowing passage of abnormal amount of current is known as a/an（）.

A.open circuit
B.short circuit
C.polarized ground
D.ground reference point

单项选择题

Which of the following statements represents the main difference between a relay and a contactor?（）

A.Contactors control current and relays control voltage
B.A relay is series connected and a contactor is parallel connected
C.Contactors can handle heavier loads than relays
D.Contactors are made from silver and relays are made from copper