The correct answer is B) Sound only fog signals until the other vessel is sighted. The reasoning behind this is that under the International and Inland Navigation Rules, when operating in restricted visibility, vessels are required to sound appropriate fog signals to indicate their presence and maneuvers. Sounding two prolonged blasts on the whistle indicates that the other vessel is changing course to the right. In this situation, you should respond by sounding your own fog signals, such as one prolonged blast, to communicate your presence, but you should not sound any maneuvering signals until you have visually identified the other vessel. Sounding maneuvering signals without being able to see the other vessel could lead to a collision. The other options are incorrect because A) is not required, C) does not provide the necessary communication, and D) could result in a collision if the vessels are not properly coordinated.