断路器的作用包括（  ）。 

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SQL Error: select id,body,options from ***_enewstiku_ where sourceid='69484' and id < 4500577 and id<>'4500577' order by id desc limit 5 SQL Error: select id,body,options from ***_enewstiku_ where sourceid='69484' and id > 4500577 and id<>'4500577' order by id asc limit 5