Explanation:

- Option 1: Parsons

- Talcott Parsons, an American sociologist, is known for developing the action theory and structural functionalism. However, he built upon many ideas initially explored by earlier sociologists, such as Weber.

- Option 2: Merton

- Robert K. Merton was an American sociologist famous for theories like the "self-fulfilling prophecy" and the "unintended consequences." He did not introduce social action as a primary subject matter.

- Option 3: Max Weber

- Max Weber is known for introducing the study of social action in sociology. He focused on understanding human behavior and the reasons behind actions within a social context.

- Option 4: None

- This option would imply that none of the listed people introduced the study of social action, which is incorrect as Weber is credited for doing so.