单项选择题
A.DC45~130V B.AC110V C.DC24~50V D.交直流两用
A.3000Hz B.2250Hz C.2288Hz D.2289Hz
A.同频单工 B.异频单工 C.双工状态 D.半双工
A.80% B.98% C.99% D.100%
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