The correct answer is B) Restrains the container against horizontal motion. A bridge fitting is a metal fitting on the container that is used to lash and secure the container to the deck of the ship. The primary purpose of a bridge fitting is to restrain the container against horizontal motion, preventing it from sliding or shifting during the voyage. This is an important safety feature to ensure the stability and security of the container cargo. The other answer choices are incorrect because: A) Racking loads are restrained by other lashing methods, not specifically the bridge fitting. C) The entire container stack is typically lashed together, not just the bridge fitting. D) The containers are lashed directly to the deck, not to the container below.