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單項選擇題

Variation in a compass is caused by（）.

A.Worn gears in the compass housing
B.Magnetism from the earth's magnetic field
C.Magnetism within the vessel
D.Lack of oil in the compass bearings

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單項選擇題

This induced magnetism（）the permanent magnetism already present in the ship.

A.will add to
B.will subtract from
C.may add to or subtract from
D.will not change

單項選擇題

The variation for most given areas undergoes（）change，the amount of which is also noted on charts.

A.an annual
B.a constant
C.a variable
D.an unstable

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