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 use of this rule does not relieve vessels（）their obligations to comply with the local laws.
单项选择题 The vessel ahead（）you is stopped.
单项选择题 The weather is often（）in a high-pressure area.
