单项选择题
The recording fathometer produces a graphic record of the（）.
A.bottom contour only up to depths of 100 fathoms B.depth underneath the keel against a time base C.contour of the bottom against a distance base D.depth of water against a distance base
单项选择题 The points on the earth’s surface where the magnetic dip is 90° are（）.
单项选择题 The four standard light colors used for lighted aids to navigation are red，green，white，and （）.
单项选择题 The equator is（）.
