单项选择题
How is the annual rate of change for magnetic variation shown on a pilot chart?（）
A.Gray lines on the uppermost inset chart B.Red lines on the main body of the chart C.In parenthesis on the lines of equal magnetic variation D.Annual rate of change is not shown
单项选择题 In which source could you find the number of a chart for a certain geographic area?（）
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 （）.
