单项选择题
The transmission of messages respecting the dangers specified is free（）cost to the ships concerned.
A.of B.on C.at D.in
单项选择题 The towing light is a(n)（）.
单项选择题 The term OIL as used in the Oil Pollution Regulations means（）.
单项选择题 The radiotelephone safety message urgently concerned with safety of a person would be prefixed by the word（）.
