先导通道的形成是以（   ）的出现为特征。

试卷相关题目

SQL Error: select id,body,options from ***_enewstiku_ where sourceid='68449' and id < 4418919 and id<>'4418919' order by id desc limit 5 SQL Error: select id,body,options from ***_enewstiku_ where sourceid='68449' and id > 4418919 and id<>'4418919' order by id asc limit 5