The correct answer is B) help keep the deck dry. A bulwark is a vertical wall-like structure that extends above the main deck of a vessel. Its primary function is to prevent water from washing onto the deck, keeping it dry and improving the vessel's stability and seaworthiness. This is especially important for smaller vessels that may encounter waves or rough seas. The other answer choices are incorrect because they do not accurately describe the main function of a bulwark. A bulwark does not directly protect against twisting forces, reinforce side stringers, or prevent stress concentrations on the stringer plate. Those are different structural elements and functions within the vessel's design.