When using certain online chat programs, a person can appear invisible so that others cannot see that he or she is online and
available to talk.
Based on the context of the sentence, the oxymoron "appear invisible" means that
O A. a person's safety is at risk when he or she is online.
OB. a person has created a false identity.
O.C. a person has signed out of the online chat program.
OD. a person's online presence is unknown.