单项选择题
A.Induced magnetism in vertical soft iron
B.Induced magnetism in horizontal soft iron
C.Permanent magnetism in ship's steel
D.Vessel's inclination from the vertical
单项选择题 In more recent years，（）has been used by civilians in many new ways to determine positions，such as in automobile and boat navigation，hiking，emergency rescue，and precision agriculture and mining.
单项选择题 By convention，the north seeking ends of a compass’ magnets are colored（）.
单项选择题 Any piece of metal on becoming magnetized will develop regions of concentrated magnetism called（）.