The correct answer is B) The efficiency decreases. When an anchor is moved from sand to mud, its holding power and efficiency typically decrease. Sand provides a more stable and firm surface for the anchor to grip, allowing it to dig in and hold the vessel securely. In contrast, mud is a softer and more pliable substrate, which can make it more difficult for the anchor to establish a strong hold. As a result, the anchor's ability to resist the forces acting on the vessel, such as wind and currents, is reduced, leading to a decrease in its overall efficiency. The other options are incorrect because: A) The efficiency does not increase when the anchor is moved from sand to mud. C) The efficiency cannot remain the same, as the change in substrate affects the anchor's holding power. D) The efficiency can be determined based on the principles of anchor behavior in different substrates.