单项选择题

Which of the following statements is true concerning all three-phase alternators?（）

A.Each has three separate but identical armature windings acted on by one system of rotating magnets
B.Each has one armature winding acted on by three identical but separate systems of rotating magnets
C.All three-phase alternators are designed to operate with a O8 leading power factor
D.The three phases always provide power to the load through three sets of slip rings and brushes

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