单项选择题 Any piece of metal on becoming magnetized will develop regions of concentrated magnetism called（）.

单项选择题 A vessel is heading magnetic east and its magnetic compass indicates a heading of 086°.Which action should be taken to remove this error during compass adjustment（）.

单项选择题 A ship under construction or major repair will acquire permanent magnetism due to（）while sitting stationary in the earth’s magnetic field.