在Internet中，用字符串表示的IP地址称为()。
A．账户
B．域名
C．主机名
D．用户名
参考答案：B
解析：为便于记忆，用域名表示IP地址。
A．It makes them noisier than they were 20 years ago.
B．It makes it difficult for them to fall asleep.
C．It affects their work during the day.
D．It does harm to their hearing.
什么情况下，航空公司可以不为某机型专门制作相应机场跑道的起飞一发失效应急程序？
