在一个心动周期中，二尖瓣开放始于（      ）

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SQL Error: select id,body,options from ***_enewstiku where sourceid='25935' and id < 2179398 and id<>'2179398' order by id desc limit 5 SQL Error: select id,body,options from ***_enewstiku where sourceid='25935' and id > 2179398 and id<>'2179398' order by id asc limit 5