单项选择题
The magnetism in the various structures of a ship changing as a result of cruising，vibration，or aging is termed（）.
A.permanent magnetism B.subpermanent magnetism C.induced magnetism D.variable magnetism
单项选择题 The line which connects the points of zero magnetic dip is（）.
单项选择题 The Flinders bar and the quadrantal spheres should be tested for permanent magnetism at what interval（）.
单项选择题 The Flinders bar on a magnetic compass compensates for the（）.
