SDH中常用的复用段保护环有哪些？
参考答案：
两种：二纤双向复用段共享保护环和四纤双向复用段共享保护环。
In a data communication system, which transport media can be described as following: Has two classes: single mode and multiple mode; with higher transmit rate; with the best reliability
A．radio channel
B．fiber optic cable
C．twisted-pair cable
D．coaxial cable
马铃薯品种陇薯5号的栽培要点有哪些？
