The correct answer is D) made by placing two bulkheads a few feet apart. A cofferdam is a temporary watertight enclosure built within a ship's hull or around an opening in a ship, typically used to allow repairs or maintenance to be carried out below the waterline. It is created by placing two bulkheads (vertical partitions) a few feet apart, effectively creating a small enclosed space that can be dewatered to access the area between the bulkheads. The other answer choices do not accurately describe a cofferdam. A) refers to a structural member, B) describes a deck, and C) describes a different type of structural beam, none of which are the same as the definition of a cofferdam.