The correct answer is C) One prolonged and three short blasts. According to the International and Inland Navigation Rules, a vessel engaged in towing another vessel should sound the following signals when operating in restricted visibility (fog): - The towing vessel: One prolonged blast followed by two short blasts, in that sequence, repeated at intervals of not more than 2 minutes. - The last vessel of the tow: One prolonged blast followed by three short blasts, in that sequence, repeated at intervals of not more than 2 minutes. This signal pattern helps other vessels in the vicinity identify the tow and its direction of movement, which is crucial for safe navigation in restricted visibility. The other options are incorrect because they do not match the specific signal pattern required for the last vessel of the tow as per the Navigation Rules.