The correct answer is A) Excessively fouled boiler economizer gas side. The reasoning is that a fouled economizer on the gas side would reduce the heat transfer to the feed water, resulting in a lower than normal feed water temperature. This would also increase the furnace pressure as the boiler would need to work harder to generate the required steam, and the higher furnace pressure would in turn lead to a higher superheater temperature. The other options are incorrect because: B) a fouled superheater would not affect the feed water temperature, C) too much excess air would not cause the specific symptoms described, and D) a fouled water screen would not directly impact the feed water temperature or superheater temperature.