The basic concept of GMDSS is（）.

A.Search and rescue authorities ashore will rapidly received an distress alert and acted upon

B.SAR units will be rapidly alerted to a distress incident and assist in a coordinated SAR operation

C.Ships navigating in the immediate vicinity of the ship in distress will rapidly alerted to the alert and give their help accordingly

D.The RCC will rapidly alerted to a distress alert through satellite and terrestrial communication techniques and conducted a rescue operation immediately