The correct answer is A) deck line. Freeboard is measured from the upper edge of the deck line, which is the boundary between the deck and the side of the vessel. This is the standard measurement used to determine the distance between the waterline and the upper edge of the main deck, as specified in the regulations governing the U.S. Coast Guard Captain's License Examinations. The other options are incorrect because the gunwale bar, sheer strake, and bulwark are not the primary reference points for measuring freeboard. These are structural components of the vessel, but do not directly define the freeboard measurement.