旋风除尘器是利用含尘气体高速旋转产生的（）将粉尘从气体中分离出来的除尘设备。
参考答案：离心力
小题1:I was writing a letter when my mother got home. (对划线部分提问)
___________ ___________ you doing when your mother got home?
小题2:Could you give the book back to the school library tomorrow? (改为同义句)
Could you __________ the book __________ the school library tomorrow?
小题3:“Are you mad at your sister?” Mary said to me. （改为间接引语）
Mary asked me ___________ I _____________ mad at my sister.
小题4:当我们遇到麻烦时，我们应该向警察寻求帮助。（完成译句）
We should the police help when we are in trouble.
据NetworkWilards公司公布的最新调查结果显示，截至99年1月全球联网主机的总数已增长至（）多万台。
A.1000
B.2000
C.3000
D.4000
