单项选择题
A METHOD OF TOWING VESSELS THROUGH POLAR ICE BY MEANS OF ICEBREAKING TUGS WITH A SPECIAL STERN NOTCH SUITED TO RECEIVE AND HOLD THE BOW OF THE VESSEL TO BE TOWED defines（）.
A.Towing operations B.Rigid coupled towing C.Close coupled towing D.Hard coupled towing
单项选择题 A MARK OR POSITION AT WHICH A VESSEL IS REQUIRED TO REPORT TO ESTABLISH ITS POSITION defines（）.
单项选择题 （）will the discharging operations take?
单项选择题 （）will reduce the visibility.
