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Permanent magnetism is caused by（）.

A.operation of electrical equipment and generators on board ship
B.the earth's magnetic field affecting the ship's hard iron during construction
C.the horizontal component of the earth's magnetic field acting on the horizontal soft iron
D.the vertical component of the earth's magnetic field acting on the vertical soft iron

單項選擇題

It is not necessary to declare（）in the Health List.

A.Appendicitis
B.Cholera
C.Plague
D.Typhus fever