Explanation:

- Option 1: Face to face contact

- This means people interact directly, seeing each other physically. While it enhances interaction, it is not strictly required. Social interaction can occur without being present together (e.g., letters, calls).

- Option 2: Harmony

- Social interaction doesn’t require harmony. People often interact in conflict or disagreement.

- Option 3: Physical contact

- Touch or physical closeness is not essential for social interaction. Many interactions are non-physical.

- Option 4: Mutual orientation

- This means both parties recognize, respond to, or are aware of each other. It's about intention, awareness, and response. This is the true pre-requisite for social interaction.