The correct answer is D) They may have lightening, limber, or air holes cut into them. Solid floors on vessels are built to be strong and durable, but they can also be heavy. To reduce the weight of the solid floors, designers often cut lightening, limber, or air holes into them. These holes allow the floors to be lighter while still maintaining the necessary structural integrity. The other answer choices are incorrect. A) is incorrect because solid floors are typically heavier than open floors. B) is incorrect because this describes the construction of structural frames, not solid floors. C) is incorrect because solid floors are not required to be watertight, unlike other vessel components.