单项选择题
A.soap hardness
B.nitrog encontent
C.chloride content
D.dissolved CO2
单项选择题 Which of the following procedures decreases the total dissolved solids concentration in the water of an auxiliary boiler?（）
单项选择题 Failure of the burner flame in an auxiliary boiler would probably be a result of（）
单项选择题 Which action should be taken when an auxiliary boiler in is operation?（）