The correct answer is C) to stiffen areas under points of great stress between beams. A carling is a longitudinal structural member that is used to reinforce and stiffen the deck of a ship, particularly in areas where there is high stress or concentrated loads, such as under heavy equipment or cargo. By providing additional support between the main deck beams, carlings help distribute the forces and prevent damage or deformation to the deck structure. The other answer choices are incorrect because they do not accurately describe the primary purpose of a carling aboard a ship. Option A refers to a cargo rig, option B is about the anchor, and option D is about connecting plating, none of which are the main function of a carling.