单项选择题
The MOST important feature of the material used for making the binnacle of a standard magnetic compass is that it is（）.
A.nonmagnetic B.weatherproof C.corrosion resistant D.capable of being permanently affixed to the vessel
单项选择题 The most accurate method of determining gyrocompass error while underway is by（）.
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（）.
单项选择题 The line which connects the points of zero magnetic dip is（）.
