How is "radio silence" imposed?

A
By the Rescue Coordination Center (RCC) controlling the distress communications on that frequency or channel
B
By the Coast Earth Station (CES) controlling the distress communications on that frequency or channel
C
By the Public Correspondence Station (PCS), controlling the distress communications on that frequency or channel
D
By the High Seas Service (HSS) controlling the distress communications on that frequency or channel.
E