The correct answer is C) S, which represents a blackwall hitch in the illustration D030DG. The blackwall hitch is a type of knot used to attach a rope to a fixed object, such as a cleat or a ring. It is a common knot used in various maritime applications, including docking and mooring. The illustration clearly depicts the blackwall hitch as the "S" knot, confirming that C is the correct answer. The other answer choices (A, B, and D) do not represent the blackwall hitch in the given illustration.