According to the air traffic rules you should your mobile phone before boardingA. switch

问题补充：

According to the air traffic rules，you should your mobile phone before boarding．

A. switch over

B. switch on

C. switch off

D. switch round

答案：

A. switch over

B. switch on

(答案→)C. switch off

D. switch round

解析：本题考查短语辨析。switch off关闭；switch over转变；switch on打开；switch round改变。句意：根据空中交通规则，你应当在降落之前把你的移动电话关闭。