问题详情

The correct procedure for giving an auxiliary boiler a bottom blow, is to begin .

A.when the boiler has been secured long enough for most solids to settle

B.when the boiler has been cooled to ambient temperature

C.only after raising the water level to within 0.5 inch of the high water cutout only

D.after bypassing the low pressure

请帮忙给出正确答案和分析，谢谢！