单项选择题
In which source could you find the number of a chart for a certain geographic area?（）
A.Chart No.1 B.Catalog of Charts C.IMO Practical Navigator D.IMO Light List
单项选择题 Isogonic lines are lines on a chart indicating （）.
单项选择题 Lines on a chart which connect points of equal magnetic variation are called （）.
单项选择题 Many of the soundings shown on the chart are derived from （）.Undue reliance should not be placed upon them．
