ADM是一个()设备,它的输出和输入均为STM-N光信号,支路信号可以是同步的,也可以是准同步的。
A.四端口
B.三端口
C.二端口
D.单端口
参考答案:B
— Look! The black clouds are gathering, which indicates that it __________ rain soon.
— Yes, black clouds are the _________ of the rain. [ ]
A. is going to; signal
B. will; mark
C. is gong to; sign
D. is to; sign
按环境要素不同环境污染可分为______。
A.物理污染
B.大气污染
C.化学污染
D.水体污染
E.土壤污染