单项选择题
The effectiveness of the action shall be carefully checked until the other vessel is finally （）.
A.past B.clear C.past or clear D.past and clear
单项选择题 Sailing vessels are stand-on over power-driven vessels except（）.
单项选择题 Risk of collision is considered to exist if（）.
单项选择题 Power-driven vessels must keep out of the way of sailing vessels except（）.
