具有磁力制动的差动继电器由哪些元件组成?(   )

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SQL Error: select id,body,options from ***_enewstiku_ where sourceid='69519' and id < 4503822 and id<>'4503822' order by id desc limit 5 SQL Error: select id,body,options from ***_enewstiku_ where sourceid='69519' and id > 4503822 and id<>'4503822' order by id asc limit 5