The correct answer is B) Intercostal. In the illustration, the structural member indicated by the letter K is fitted in segments between continuous longitudinals. This type of structural member is known as an intercostal floor. Intercostal floors are floors that are not continuous, but rather fitted in between the continuous longitudinal members of the ship's structure. The other answer choices are incorrect because: A) Lightened floors refer to floors with openings or lightening holes to reduce weight, C) Non-watertight floors are not designed to be watertight, and D) Open floors have large openings that make them unsuitable for providing structural support.