The correct answer is C. A vessel displaying these load line markings may load in the salt waters of the St. Lawrence River. The load line markings shown in the illustration indicate that the vessel is assigned a load line, which allows it to load up to a certain draft when operating in salt water. This allows the vessel to safely carry more cargo while maintaining appropriate stability and seaworthiness. Vessels engaged solely on Great Lakes voyages (option B) are not required to have these load line markings, and vessels under 100 feet and 200 gross tons (option A) are also exempt. However, U.S. flag vessels of 100 gross tons and upward (option D) are required to display these load line markings.