正常心脏起搏点是窦房结，其冲动产生的频率是（ ）

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SQL Error: select id,body,options from ***_enewstiku where sourceid='28307' and id < 2316488 and id<>'2316488' order by id desc limit 5 SQL Error: select id,body,options from ***_enewstiku where sourceid='28307' and id > 2316488 and id<>'2316488' order by id asc limit 5