Out of the human relations skills, the one that is most clearly related to communication is the skill of listening.
Explanation:
Human relations are the ultimate result of the preluding process of communication that happens among humans. When a vocal-verbal communication is two way, it involves the actions of speaking and listening.
Listening allows the communicating parties to understand the message conveyed by the other party. A two-way vocal-verbal communication is thus impossible without the action of listening.