Explanation:

Let’s break down each option:

- Option 1: Goal

Having a goal helps, but just setting a goal isn’t enough for true interaction. Two people with goals might never interact at all.

- Option 2: Motivation

Motivation makes interaction more likely, but you could have motivation and still not actually interact with someone.

- Option 3: At least two actors talking of each other

This is getting closer, but just talking about each other isn’t interacting. You could gossip behind someone’s back and never truly interact.

- Option 4: Mutual reciprocity

Here’s the thing—interaction is about a two-way street. It’s not interaction unless both sides are responding, reacting, or influencing back and forth. That’s mutual reciprocity.

So, out of these, the must-have ingredient for interaction is mutual reciprocity. Without that back-and-forth, it’s just noise.