单项选择题
A.head-on situation
B.end-situation
C.crossing situation
D.close-quaters situation
单项选择题 When in sight of another vessel，any action taken to avoid collision must（）.
单项选择题 When two power-driven vessels are meeting on reciprocal or nearly reciprocal courses so as to involve risk of collision，they shall be deemed to be in（）.
单项选择题 When you doubt the existence of risk of collision,（）.