单项选择题 If a towing vessel and her tow are severely restricted in their ability to change course，they may show lights in addition to their towing identification lights. These additional lights may be shown if the tow is（）.

单项选择题 How does the effect known as bank suction act on a single-screw vessel proceeding along a narrow channel?（）.

单项选择题 For the deepest water when rounding a bend in a river，you should navigate your vessel（）.