单项选择题

A direct current passing through a wire coiled around a soft iron core is the description of a simple（）.

A.magnetic shield
B.electromagnet
C.piezoelectric device
D.electromagnetic domain

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A resistance in a circuit of unknown value is to be tes...

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An accidental path of low resistance, allowing passage ...

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船舶电气与船舶安全

A direct current passing through a wire coiled around a soft iron core is the description of a simple（）.