Explanation:

- Parsons: He introduced the concept of "Pattern Variables," a framework used to understand social actions and choices based on patterns in roles and institutions.

- Marx: Karl Marx focused on class struggle, capitalism, and historical materialism.

- Merton: Known for theories like the "self-fulfilling prophecy" and "role model," but not "Pattern Variables."

- Weber: Studied social organization and bureaucracy but did not develop "Pattern Variables."

Parsons is the correct answer.