The correct answer is A) You need not sound any whistle signals. The reasoning for this is that under the Inland Navigation Rules, which govern inland waterways in the United States, there is no requirement to sound whistle signals when a power-driven vessel is putting its engines full speed astern, as long as the other vessel is more than 0.5 mile away and forward of your beam. The whistle signals are only required when vessels are meeting, crossing, or overtaking each other, which is not the case in this scenario. The other options are incorrect because B) sounding three short blasts is only required when a vessel is backing astern, C) sounding one blast is for turning to starboard, and D) whistle signals are not required solely because the vessels are in sight of each other.