The correct answer is C) Vessel restricted in her ability to maneuver. According to the International Regulations for Preventing Collisions at Sea (COLREGS), a vessel restricted in her ability to maneuver is defined as a vessel that, from the nature of her work, is unable to keep out of the way of another vessel. This includes vessels such as dredgers, cable layers, and research ships. These vessels have limited maneuverability and are unable to readily change course or speed to avoid a collision, and thus have the right-of-way over other vessels. The other answer options are incorrect because a vessel towing (A) is required to keep out of the way of a sailing vessel (B) or a vessel engaged in fishing (D), as these vessels are considered to have a reduced ability to maneuver.