单项选择题
Proper combustion in a boiler would be indicated by （）.
A.yellowish flame B.golden yellow flame C.white flame D.brilliant white flame
单项选择题 Black smoke coming from a boiler can be caused by （）.
单项选择题 Which of the following pumps belongs to centrifugal pump?（）
单项选择题 The advantage of a centrifugal pump as compared with a reciprocating pump is that （）.
