What are the requirements for breeders, suppliers, and users to be authorized according to Article 20?
I. Compliance with the requirements of this Directive.
II. Registration with the competent authority.
III. Authorization granted for an unlimited period of time.
IV. Renewal of authorization required for any significant change in the structure or function of the establishment.

a) I and II are correct.
b) II and III are correct.
c) I, II, and IV are correct.