The correct answer is C) Shrouds and stays. Shrouds and stays are the standing rigging that support the mast in the fore-and-aft and athwartships directions. Shrouds run from the mast to the sides of the vessel, providing lateral support, while stays run from the mast to the bow and stern, providing fore-and-aft support. This configuration is in accordance with standard rigging practices and is the most effective way to stabilize the mast and prevent it from moving in any direction. The other options are incorrect because: A) Guys and vangs are primarily used for controlling the shape and tension of sails, not for supporting the mast; B) Vangs and shrouds do not provide the necessary support in both the fore-and-aft and athwartships directions; and D) Sheets and guys are not considered standing rigging and are used for controlling the position and trim of sails, not for mast support.