单项选择题
A.adding hydrazine
B.blowing down the boiler
C.adding phenolphthalein
D.adding a sulfite chloride scavenger
单项选择题 The purpose of designing some waste heat boilers with sinuous fire tubes, is to（）
单项选择题 The water in an auxiliary boiler should be chemically tested daily for alkalinity and（）
单项选择题 Which of the following procedures decreases the total dissolved solids concentration in the water of an auxiliary boiler?（）