车辆在高速公路行驶，当高速公路上有限速交通标志的，车辆应当按照（）所示时速行驶。

频率大于　　　HZ的声波为超声波。为了保护听力，声音不能超过　　　　dB。

下列实验不正确的是（　　）

A．A

B．B

C．C

D．D

2.5÷22的商是______小数，保留两位小数是______．

—What are people supposed to do when they meet in China?        

—People are supposed to           when they meet for the first time.[ ]

A. kiss

B. shake hands

C. bow

D. embrace

—How often do you go to the old people’s house, Tom?

—________.[ ]

A. Once a month

B. In a month

C. After a month

D. For a month