单项选择题
A.红、黄、绿 B.黄、绿、红 C.绿、黄、红 D.黄、黄、红
A.负序 B.正序 C.零序 D.反序
A.60° B.30° C.90° D.180°
A.π/2 B.π/3 C.π/2f D.π/3f
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