单项选择题
A.treating with oxygen scavengers
B.securing the boiler and giving it a blowing down
C.increasing the pH
D.reducing the phosphate level
单项选择题 Excessive alkalinity of the water in an auxiliary boiler can cause （）.
单项选择题 The purpose of the delivery check valve used in a diesel fuel injection jerk pump is to （）.
单项选择题 Before an auxiliary boiler is shutdown for an extended period of time, the water in the boiler should have a pH value of （）.