The correct answer is D) Fisherman's bend. The Fisherman's bend is the knot best suited for attaching a line to the ring of an anchor on a small boat. This knot is strong, secure, and able to resist slipping, making it the preferred choice for this application. The Fisherman's bend creates a reliable connection that can withstand the pulling forces exerted on the anchor line. The other options are not as well-suited for this purpose. The overhand knot (A) and figure-eight knot (C) are generally used for different applications, while the clove hitch (B) may not provide the same level of security and stability when attached to an anchor ring.