单项选择题
The operation of which aids to navigation may be suspended during war or national emergency（）.
A.Navigational satellites B.Loran C.Omega D.Any of the above
单项选择题 The loran lines drawn on navigation charts represent（）.
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（）.
