单项选择题 Which one is not the normal operation for boiler shutdown?（）

单项选择题 The forced draught fan should be started and air passed through the furnace for several minutes to “（）” it of any exhaust gas or oil vapors.

单项选择题 A shallow dish positioned at the normal water level is connected to the（）This enables the blowing down or removal of scum and impurities from the water surface.