单项选择题
A.A power-driven vessel B.A vessel engaged on pilotage duty C.A vessel dredging D.A vessel restricted in her ability to maneuver
While underway，in fog，you hear a whistle signal of one ...
单项选择题While underway，in fog，you hear a whistle signal of one prolonged blast followed by two short blasts. This signal is sounded by a vessel（）.
A.not under command B.being towed C.on pilotage duty D.aground
