What is retroalimentación in the endocrine system?

Retroalimentación is the way in which the message is encoded to allow its diffusion.
Retroalimentación is the element that receives the signal and interprets the message contained in it.
Retroalimentación is the element responsible for responding to a message by carrying out an action.
a) Only I is correct.
b) Only II is correct.
c) Only III is correct.
d) I and II are correct.
e) II and III are correct.