The correct answer is D) steam velocity aids in the atomizing of fuel oil over a wide range of fuel pressures. In boilers equipped with steam atomizers, the steam velocity helps to break up the fuel oil into a fine mist or atomized spray, even as the fuel oil pressure varies across different load ranges. This allows the boiler to operate over a wide load range without the need to cut burners in and out, as the steam velocity compensates for changes in the fuel oil pressure. The other options are incorrect because: A) the atomizing steam pressure is not held constant, but rather varies with the load; B) the steam does not necessarily maintain the oil at the fire point temperature; and C) regulating the fuel oil pressure at the burners is still necessary, but the steam velocity aids in the atomization process.