单项选择题 A vessel not to impede the passage of another vessel is not relieved （） taking collision-avoiding action.

单项选择题 A vessel is entering port A for the first time and has a Pilot conning the vessel. The Master is unsure that the Pilot is taking sufficient action to prevent a collision. What should the Master do（）.

单项选择题 A tug is to assist in docking an oceangoing vessel on a hawser. The greatest danger to the tug is （）.