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单选题
A circuit breaker differs from a fuse in that a circuit breaker （）.
A
melts and must be replaced
B
is enclosed in a tube of insulating material with metal ferrules at each end
C
gives no visual indication of having opened the circuit
D
trips to break the circuit and may be reset
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单选题A circuit breaker and a fuse have a basic similarity in that they both （）.A
can be reset to energize the circuitB
should open the circuit when overloadedC
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考题
单选题A circuit breaker differs from a fuse in that a circuit breaker （）.A
melts and must be replacedB
is enclosed in a tube of insulating material with metal ferrules at each endC
gives no visual indication of having opened the circuitD
trips to break the circuit and may be reset
考题
单选题You are attempting to parallel two AC generators, and the syncope pointer is revolving in the fast directionThis indicates that the frequency of the incoming machine is （）.A
higher than the bus frequencyB
lower than the bus frequencyC
the same as the bus frequency but out of phase with itD
the same as the bus frequency and the circuit breaker may be closed at any pointer position
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多选题Which two of these are characteristics of Metro Ethernet? （）Aclass of serviceBbandwidth profilesCuser-network interfaceDEthernet LAN circuit attributesEEthernet virtual circuit attributes
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