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單項(xiàng)選擇題

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

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單項(xiàng)選擇題

The safety valve should be （） in the presence of C/E and Surveyor.

A.tightened up
B.sealed up
C.opened up
D.unscrewed

單項(xiàng)選擇題

The safety valves are mounted in pairs to （） the boiler against overpressure.

A.use
B.release
C.protect
D.effect