单项选择题
Between the steam dram and the smaller water dram below, large numbers of smaller diameter （） tubes are fitted.
A.fire B.water wall C.generating D.down comer
单项选择题 The safety valve should be （） in the presence of C/E and Surveyor.
单项选择题 The safety valves are mounted in pairs to （） the boiler against overpressure.
单项选择题 The defective place in the furnace should be （） with fire bricks.
