The correct answer is B) two short blasts. According to the Inland Navigation Rules, when overtaking another power-driven vessel and desiring to pass on the left or port side, the vessel overtaking must sound two short blasts to indicate their intention to pass. This signal alerts the other vessel that you are planning to overtake and pass them on their port side. The other answer choices are incorrect because: A) one long blast is the signal to indicate you are departing a dock or berth, C) two prolonged blasts followed by two short blasts is the signal to indicate you are crossing another vessel's bow, and D) one short blast is the signal to indicate you are altering your course to starboard.