湿球结冰,当湿度很大,风速很小时,应在观测前()分钟内进行溶冰。
A.30
B.20
C.50
参考答案:C
The old lady is very healthy because she often . [ ]
A. plays
B. drinks
C. sleeps
D. exercises
交换式局域网增强带宽的方法是在交换机多个端口之间建立______。