Don’t come in unless ________
A.invitingB.inviting toC.invited toD.being invited to在线课程C
考查省略。句意“不要进来，除非（你）被邀请。”即unless you are invited to...；“邀请某人做某事”invite sb. to do sth.，被动形式是sb. Be invited to do sth.。故选C。