The correct answer is A) refractory and insulation. Downcomers on auxiliary package boilers are protected from direct contact with hot gases through the use of refractory and insulation materials. These materials create a barrier that prevents the hot gases from coming into direct contact with the downcomers, which are the vertical tubes that carry the water or steam from the steam drum to the mud drum. The refractory and insulation help to maintain the integrity of the downcomer system and ensure safe operation of the boiler. The other answer choices are incorrect because they do not accurately describe the method used to protect downcomers from hot gases on auxiliary package boilers. Steel baffles, screen tubes, and water wall tubes are not the primary means of protecting downcomers in this type of boiler configuration.