单项选择题
A.engaged on pilotage duty
B.in distress
C.at anchor
D.being overtaken in a narrow channel
单项选择题 A signal of intent must be sounded in international waters by（）.
单项选择题 A sailing vessel shall not impede the safe passage of a（）.
单项选择题 A sailing vessel is overtaking a power-driven vessel in a narrow channel，so as to pass on the power-driven vessel’s port side. The overtaken vessel will have to move to facilitate passage. The sailing vessel is the（）.