According to the GDPR, what is a task of a supervisory authority?

Implement technical and organizational measures to ensure compliance. Incorrect. This is the task of the controller.

Investigate security breaches of corporate information. Incorrect. Only breaches of personal data are a concern of the supervisory authority.

Monitor and enforce the application of the GDPR. Correct. This is the main task of any supervisory authority. (Literature: A, Chapter 7)