单项选择题
The operator of the ship’s radiotelephone，if the radiotelephone is carried voluntarily，must hold at least a（）.
A.Mate's license B.Restricted radiotelephone operator permit C.Second-class radio operator's license D.Seaman's document
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（）.
单项选择题 The line connecting the Loran-C master station with a secondary station is called the（）.
