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單項選擇題

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

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

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單項選擇題

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

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

單項選擇題

The defective place in the furnace should be （） with fire bricks.

A.paved
B.cleaned
C.welded
D.dismantled