单项选择题
When a pushing vessel and a vessel being pushed are rigidly connected in a composite unit，they shall be regarded as（）.
A.a tugboat B.a sailing vessel C.a power-driven vessel D.a vessel propelled by machinery and under sail
单项选择题 What determines if a vessel is restricted in her ability to maneuver?（）.
单项选择题 Vessels shall be deemed to be in sight of one another only when one（）from the other.
单项选择题 Vessel underway means that a vessel is（）.
