单项选择题
The receiver uses（）satellites to compute latitude，longitude，altitude，and velocity．
A.one B.two C.three D.four
单项选择题 The operator of the ship’s radiotelephone，if the radiotelephone is carried voluntarily，must hold at least a（）.
单项选择题 The operation of which aids to navigation may be suspended during war or national emergency（）.
单项选择题 The loran lines drawn on navigation charts represent（）.
