The correct answer is B) roll. Angular motion about the longitudinal axis of a vessel is known as roll. This is because the longitudinal axis runs from the bow to the stern of the vessel, and rotation or angular motion around this axis is defined as roll. The other options, sway (lateral motion), pitch (angular motion about the transverse axis), and surge (linear motion along the longitudinal axis), do not accurately describe the angular motion being referred to in the question.