If the radio signal ground wave extends out for less distance than the minimum skywave distance，there is an area in which no signal is received．This is called the（）.

A.provide safety-related information automatically to shore stations，other vessels and aircraft
B.receive safety-related information automatically from similarly equipped vessels
C.exchange safety-related information with shore-based facilities
D.All of the above

A.He space component
B.Control component
C.User component
D.Alarming component

A.Deviating from a planned route
B.Approach to waypoints and other critical points
C.Light house detecting
D.Larger scale chart available