直肠上、下静脉丛在何处互相交通:() ["齿线","栉膜带","肛门白线","肛管直肠环","以上均不对"]
齿线上的痔内静脉丛分布在何处最为显著:() ["左前、右后、左侧","右前、左前、左侧","右侧、右后、左前","右前、右后、左侧","左前、左后、右侧"]
简述我国将森林划分为哪几大林种。
肛门直肠的血液供应主要来自除外下列哪一动脉:() ["阴部内动脉","直肠下动脉","直肠上动脉","肛门动脉","骶中动脉"]
肛管的长度是:() ["2cm","3cm","4cm","5cm","6cm"]
简述苗期管理的内容。