单项选择题
A.tightened up B.sealed up C.opened up D.unscrewed
The safety valves are mounted in pairs to （） the boiler...
单项选择题The safety valves are mounted in pairs to （） the boiler against overpressure.
A.use B.release C.protect D.effect
The defective place in the furnace should be （） with fi...
单项选择题The defective place in the furnace should be （） with fire bricks.
A.paved B.cleaned C.welded D.dismantled
The exhaust boilers are used to recover some of （） carr...
单项选择题The exhaust boilers are used to recover some of （） carried in the exhaust gas from the main engine.
A.water B.oil C.heat D.steam
