单项选择题
A.after the point is reached at which the failures begin to increase rapidly
B.before the point is reached at which the failures begin to increase rapidly
C.before the point is reached at which the failures begin to increase slowly
D.after the point is reached at which the failures begin to increase slowly
单项选择题 With （）, the corrosion problems are much reduced in a central cooling system.
单项选择题 You must take good care of the drainage cock of the air control systemBecause （） leads scale formed which might malfunction the pilot control valve and other instruments.
单项选择题 You increased the （） to 150 tons that’s why the fuel oil （）.