The correct answer is B) Superheater. In a water-tube marine boiler, the steam generated in the generating tubes (also called the steam drum) is further heated in the superheater section of the boiler. The superheater uses the hot flue gases from the firebox to increase the temperature of the steam, making it superheated. This superheated steam is then delivered to the engine or turbine at a higher temperature, which improves the efficiency of the system. The other options are incorrect because: A) The economizer preheats the boiler feed water, but does not increase the temperature of the steam. C) The firebox is where the fuel is burned to generate the heat, but it is not the part where the steam temperature is increased. D) The mud drum is where water and sediment collect at the bottom of the boiler, and it does not play a role in increasing the steam temperature.