单项选择题
All straight lines represent great circle tracks on a chart based on a(n) （）.
A.Mercator projection B.polyconic projection C.orthographic projection D.gnomonic projection
单项选择题 Chart correction information is NOT disseminated through the （）.
单项选择题 Charted depth is the （）.
单项选择题 How is the annual rate of change for magnetic variation shown on a pilot chart?（）
