单项选择题
A.provide a means of draining the boiler
B.warn the engineer of low water level
C.cool the crown sheet at high firing rates
D.open the burners electrical firing circuits
单项选择题 In comparison to exhaust valves, intake valves of diesel engines may be fabricated from low alloy steels because （）.
单项选择题 What preventative maintenance should be done frequently to diesel engine starting air receivers?（）
单项选择题 Crank web deflection readings will give a positive indication of （）.