钢轨标志有两种类型:一种是辊轧字,另一种为热轧凹字（）

A.110、6、100%/120%/140%/160%/180%/200%
B．110、6、100%/110%/120%/130%/140%/150%
C．113、6、100%/110%/120%/130%/140%/150%
D．113、6、100%/120%/140%/160%/180%/200%

A.50
B．70
C．60
D．45

A、实轴上的根轨迹
B、根轨迹渐近线
C、根轨迹的出射和入射角
D、根轨迹的分支数