99色精品-9色在线-99色在线-99色视频国产欧美日产一区二区三区_亚洲精品亚洲人成在线观看_四虎在线精品永久观看_免费一级a一片久久精

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

你可能感興趣的試題

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