我国电力系统的额定频率为(    )

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SQL Error: select id,body,options from ***_enewstiku_ where sourceid='69497' and id < 4501889 and id<>'4501889' order by id desc limit 5 SQL Error: select id,body,options from ***_enewstiku_ where sourceid='69497' and id > 4501889 and id<>'4501889' order by id asc limit 5