单项选择题 In boilers, besides maintaining the burner atomizers, air diffuser vanes, fuel temperature, forced draft fan, fuel pump and other hardware in good condition, there are some adjustments on the （）that can produce a good flame for the most efficient operation.

单项选择题 The oil sludge is burnt in the （）on board I’ll show you the ashes.

单项选择题 Before dismantling the pipe, would you （）the oil retained in the hose with （）?