单项选择题

A switchboard, for a AC electrical distribution system, will be provided with which of the following components （）.

A.Frequency meter
B.Ammeter
C.Voltmeter
D.All of the above

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单项选择题

The sub-multiple prefix “nano” (n) means （）.

A.thousandth (10 to the-3rd power)
B.millionth (10 to the-6th power)
C.billionth (10 to the-9th power)
D.trillionth (10 to the-12th power)

单项选择题

Possible phase relationships between voltage and current in an alternating current circuit include which of the following conditions?（）

A.Current and voltage may be in phase
B.Current may lead the voltage
C.Current may lag the voltage
D.All of the above

单项选择题

The resistance of a conductor varies （）

A.directly as its length and inversely as its cross-sectional area
B.inversely as its length and directly as its cross-sectional area
C.directly as its length and directly as its cross-sectional area
D.inversely as its length and inversely as its cross-sectional area