The correct answer is A) messenger line. When connecting the tow bridle to a tug, the end of the bridle is passed with a messenger line. This is the standard practice as the messenger line allows the crew to securely and safely pass the heavier tow bridle from the tug to the towed vessel. The messenger line is a lightweight line used to pull the tow bridle across, rather than trying to throw or maneuver the bridle itself. The other options are incorrect because: B) a high line is used for transferring personnel, not tow lines; C) a shot line is a lightweight line fired from a line-throwing gun, not used for this purpose; and D) a heaving line is used to throw a lightweight line to another vessel, not to pass the actual tow bridle.