The correct answer is C) Sound one short blast, turn to starboard. This is the correct action because under the International Regulations for Preventing Collisions at Sea (COLREGS), when two power-driven vessels are passing within 1/2 mile of each other, the vessel with the other on its starboard side (in this case, vessel "I") is the give-way vessel and must take early and substantial action to keep well clear of the other vessel. Sounding one short blast and turning to starboard is the appropriate action to indicate that vessel "I" is taking the required action to avoid a collision. The other options are incorrect because: A) Holding course and speed without giving a signal does not comply with the COLREGS; B) Sounding the danger signal and slowing to moderate speed is not the correct action for this situation; and D) Sounding one short blast and holding course and speed does not indicate the required action to avoid the other vessel.