单项选择题
If in doubt as to the true water level when a boiler is being oil-fired, you should （）.
A.take no measures B.extinguish the fire as soon as possible C.feed water to the boiler D.open the blow down valve
单项选择题 The boiler feed water check valves are located on the （）
单项选择题 The water level in a steaming auxiliary boiler will always （）
单项选择题 The donkey boiler may be given a bottom blow （）
