何为调速范围？
参考答案：
生产机械要求电动机提供的最高转速nmax和最低转速nmin之比称为调速范围，用字母D表示，即
18．On October 31st, known as Halloween, dozens of children ________ costumes knock at their neighbor’s doors and yell “Trick or Treat” when the door ________.
A．putting on; is open
B．dressed up in; opens
C．having on; is open
D．wearing on; open
在信息运维综合监管系统（IMS）中，告警通知不支持（）提醒。
A、闪烁
B、短信
C、弹窗
D、声音
