【名词&注释】
生理盐水(normal saline)、不锈钢管(stainless steel tube)、救生设备(survival equipment)、机动船(motor vessel)
[单选题]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