单项选择题
A line of position from a celestial observation is a segment of a （）.
A.circle of equal altitude B.parallel of declination C.parallel of altitude D.vertical circle
单项选择题 A line of position derived from a loran reading is a section of a(n) （）.
单项选择题 A light used to signal passing intentions must be an （）.
单项选择题 A light signal consisting of three flashes means （）.
