问题
选择题
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
答案：C
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。