单项选择题
Lines on a chart which connect points of equal magnetic variation are called （）.
A.magnetic latitudes B.magnetic declinations C.dip D.isogonic lines
单项选择题 Many of the soundings shown on the chart are derived from （）.Undue reliance should not be placed upon them．
单项选择题 On this chart only the principle （） to navigation are shown．
单项选择题 To agree with larger scale chart，latitudes taken from this chart should be increased （） about 8 seconds．
