The correct answer is D) The vessel downbound with a following current. According to the Inland Navigation Rules, when two power-driven vessels are meeting on the Great Lakes, Western Rivers, or other designated waters where there is a current, the vessel that is downbound with the current is required to sound the first passing signal. This is because the vessel with the following current has a greater ability to maneuver and maintain control, so it is responsible for initiating the passing procedure. The other options are incorrect because: A) Either vessel is not the correct answer, as the rules assign the responsibility to the downbound vessel; B) The vessel that is towing is not relevant to the situation described; and C) The vessel going upstream stemming the current does not have the same maneuverability as the downbound vessel.