单项选择题
A.Ground waves
B.Skywaves
C.Either ground waves or skywaves interchangeably
D.An average between ground wave and skywave positions
单项选择题 The line connecting the Loran-C master station with a secondary station is called the（）.
单项选择题 The information received by AIS will be displayed on（）.
单项选择题 The（）transmits own ship data cyclically via two defined VHF channels and receives the same data of the other ships and objects that are equipped with AIS systems.