The correct answer is B) buoys alone. The owner or Master of a towing vessel must ensure that each person directing and controlling the movement of the vessel can accurately fix the vessel's position using all available aids to navigation, including depths soundings, hydrographic contour lines, and installed navigational equipment. However, relying solely on buoys alone is not sufficient, as buoys can be moved, damaged, or unreliable. Mariners must use multiple sources of information to accurately determine a vessel's position. The other options are incorrect because: A) depth soundings and hydrographic contour lines are required, C) all available aids to navigation must be used, and D) installed navigational equipment is necessary to accurately fix the vessel's position.