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單項(xiàng)選擇題

Isogonic lines are lines on a chart indicating （）.

A.points of equal variation
B.points of zero variation
C.the magnetic latitude
D.magnetic dip

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單項(xiàng)選擇題

Lines on a chart which connect points of equal magnetic variation are called （）.

A.magnetic latitudes
B.magnetic declinations
C.dip
D.isogonic lines

單項(xiàng)選擇題

Many of the soundings shown on the chart are derived from （）.Undue reliance should not be placed upon them．

A.complete and often very poor surveys
B.correct and often very good surveys
C.inadequate and often very old surveys
D.adequate and present surveys