How to properly ask passengers to turn off mobile phone for take-off?

How to properly ask passengers to turn off mobile phone for take-off?
A.Could you please switch off your cell phone?
B.Would you please turn off your mobile phone?
C.Smoking is not allowed.
D.Remote-controlled equipment is prohibited.
正确答案： Could you please switch off your cell phone?；Would you please turn off your mobile phone?