The correct answer is B) A fishing vessel that is not making way. According to the International Regulations for Preventing Collisions at Sea (COLREGS), a fishing vessel that is not making way is not required to show its sidelights. Instead, it must display the appropriate lights and shapes for a vessel not under command. The other options, such as a vessel not under command making way (A), a sailing vessel that is becalmed (C), or a vessel engaged in underwater operations (D), do have requirements to display sidelights when making way. However, a fishing vessel that is not making way is the only one of the given choices that is exempt from the sidelight requirement.