Final answer:
The apparent sinking of a sailboat as it moves away from an observer is best described by the sailboat moving around the curved surface of the Earth, leading to the hull disappearing first and the entire boat eventually going below the horizon.
Step-by-step explanation:
The statement that best describes the apparent sinking of the sailboat is that the sailboat is moving around the curved surface of the earth. As the sailboat moves away from the observer, it appears to sink because the hull disappears first due to the curvature of the Earth, and then the mast disappears last. This phenomenon occurs because as the distance between the observer and the sailboat increases, the curvature of the Earth obstructs the bottom part of the sailboat from view while the top part remains visible for a while longer. Eventually, all parts of the sailboat disappear under the horizon as it moves beyond the observer's line of sight over the Earth's curve. This process is observed rather than the sailboat simply appearing smaller due to distance, the effects of atmospheric refraction, or changes in ocean depth due to tides.