About business etiquette, which of the following is correct? ( )

A、Businessetiquettechangedoverthepastfewdecades.
B、Tobeefficient,youcancheckyoure-mailmessagesanywhere,evenintheelevator.
C、It’sacceptabletosendlate-nightcommuniquesine-mail.
D、Wearingcasualworkattireisregardedtobe