单项选择题
Too much air in the furnace of an oil-fired boiler would be indicated by （）.
A.yellowish flame B.golden yellow flame C.white flame D.brilliant white flame
单项选择题 The feed water to the boiler will comprise （）.
单项选择题 Proper combustion in a boiler would be indicated by （）.
单项选择题 Black smoke coming from a boiler can be caused by （）.
