A.move in an opening directionB.move in a closing direc……

单项选择题One of the main purposes of refractories in a boiler furnace is to（）

A.help preheat the air for the furnaces
B.help preheat the feedwater
C.protect economizer from excessive heat
D.prevent excessive furnace heat losses

单项选择题What is the first thing you would check on taking over a watch?（）

A.the bilges
B.the periscope
C.the water level
D.the oil pressure

单项选择题Soot blowers should be used in proper sequence so that（）

A.excess stresses will not be set up in the boiler
B.the decks will not be covered with soot
C.the soot will be swept toward the uptakes
D.there will not be a loss of steam pressure

单项选择题The valve that prevents water from backing out of the boiler into the feed line is the（）.

A.bottom-blow valve
B.skin valve
C.feed-check valve
D.feed-stop valve

单项选择题The mechanical exhaust valve operation system is replaced by（）in an electronic controlled ME engine.

A.a system with a Hydraulic Power Supply (HPS) unit
B.a system with roller guides for exhaust valves
C.a system with an electronically controlled Alpha Lubricator
D.a system directly powered by electric motor