Which one is a polite rule for cell phone use?

Which one is a polite rule for cell phone use?
A.Talk on your cell phone in a restaurant.
B.Download annoying or overly loud ring tones.
C.Answer cell phone calls when you are with others.
D.Do not wear earpieces when you are not talking on the phone.
正确答案：Do not wear earpieces when you are not talking on the phone.