The correct answer is A) They are less expensive to construct because of increased access space. The double bottom design of a ship is an advantage because it provides additional space between the inner and outer bottom of the ship, which allows for better access and ease of maintenance. However, this additional space and construction complexity makes double bottom ships more expensive to build compared to single bottom ships. The other answer choices are incorrect because: B) The double bottom raises the center of gravity, which is generally not desirable for stability; C) The double bottom provides a second protective layer for the vessel's hull; and D) The double bottom structure helps distribute the buoyant forces acting on the ship's bottom.