If in doubt as to the true water level when a boiler is being oil－fired, you should _____.

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

请帮忙给出正确答案和分析，谢谢！