Explanation:

Here’s the thing: when we talk about the Systems Theory of Industrial Relations, we’re talking about John Dunlop’s work. Let’s break down the options:

- Elton Mayo: ?? He’s famous for the Human Relations Movement, not systems theory. Think Hawthorne studies.

- Karl Marx: ?? He gave us conflict theory, focusing on class struggles and capitalism—very different angle.

- John Dunlop: (green tick) He’s the one who created the Systems Theory in Industrial Relations. He looked at IR as an interrelated set of actors (employers, employees, government), the environment, and a set of rules.

- Roethlisberger: ?? Collaborated with Mayo, worked on human relations ideas, not systems theory.

So, option 3—John Dunlop—is absolutely the right answer.