SDH环网相对链状网络的优点有（）。
A.适合于广播业务
B.可节省硬件投资
C.高自愈能力
D.更高的网络安全性
参考答案：C, D
The old man lives________, but he doesn't feel________.
A．alone; lonely
B．alone; alone
C．lonely; lonely
D．lonely; alone
28．How can they expect to learn anything________they never listen?
A．when
B．until
C．unless
D．Though
