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單項選擇題

The current flowing first in one direction and then in another is called（） current.

A.an alternating
B.a rush
C.a direct
D.an exciting

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單項選擇題

Shore power must be（） during dock repair.

A.disconnected
B.switched off
C.cut off
D.connected

單項選擇題

The coil of wire rotating in the magnetic field produces the（）.

A.voltage
B.current
C.power
D.frequency