The WWNWS is a coordinated global service for the broadcast by radio of vital information on（）to marine navigation.

A.by day or at night
B.almost round the clock
C.somewhat and sometime
D.from sunrise and sunset

A.DF
B.Radar System
C.DSC System
D.COSPAS-SARSAT

A.nature of distress
B.type of assistance required
C.course and speed and time at which the information was recorded
D.A, B, C are all right