The correct answer is B) Raising the boom. Topping the boom refers to the action of raising the boom, which is the horizontal spar that extends from the mast to support the sail on a sailing vessel. Raising the boom, or "topping" it, is a common maneuver performed to adjust the sail and control the vessel's performance. The other options do not accurately describe the meaning of "topping the boom." Lowering the boom (option C) would be the opposite of raising it, and spotting the boom over the deck (option A) or swinging it athwartships (option D) are different actions that do not specifically refer to raising the boom.