单项选择题 A vessel traveling down a narrow channel，especially if the draft is nearly equal to the depth of the water，may set off the nearer side. This effect is known as（）.

单项选择题 A vessel towing astern in an operation which severely restricts the towing vessel and her tow in their ability to change course shall，when making way，exhibit（）.

单项选择题 A vessel towing a barge astern would show，at the stern（）.