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

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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。