单项选择题
In a （） boiler the hot gases from the furnace pass through the tubes while the water is on the outside.
A.water-tube B.fire-tube C.exhaust gas D.None of the above is true
单项选择题 In a （） boiler the water flows through the inside of the tubes while the hot gases pass around the outside.
单项选择题 The tube in a boiler should be blinded if found （）.
单项选择题 The internal part of boiler should be welded by yard if found （）.
