Earth is a rocky planet where there is liquid water, which is necessary for life to ________.[ ]

A. come 

 B. exist

C. stand  

D. happen

General radio communications in the global system are those between（）concerning the management and operation of the ships and may have impact on their safety.

A.SAR party and the ship in distress

B.SAR authorities and the ship in distress and survival craft

C.A ship station and any coast station

D.Ship stations and shore-based communication network