根轨迹（root locus）
参考答案：
是指开环系统某个参数由0变化到∞，闭环特征根在s平面上移动的轨迹。
It is fairly ________ in Africa for there being a group of expert musicians ________ by others who also
join in the performances.[ ]
A. regular；surrounding
B. common；surrounded
C. ordinary；surrounding
D. usual；surround
阀门型号：D341H－25DN250中，4表示（）。
A、丝节连接
B、法兰连接
C、快速连接
D、对夹连接
