单项选择题
Excessive alkalinity of the water in an auxiliary boiler can cause （）.
A.caustic embrittlement of the boiler metal
B.acidic corrosion of the boiler metal
C.hard scale deposits on the boiler tubes
D.etching of the heat exchange surfaces
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单项选择题
The purpose of the delivery check valve used in a diesel fuel injection jerk pump is to （）.
A.assist in a quick cutoff of fuel injection
B.allow oil backflow from the injector to the helix
C.reduce fuel oil pressure between injection strokes
D.meter the quantity of fuel delivered -
单项选择题
Before an auxiliary boiler is shutdown for an extended period of time, the water in the boiler should have a pH value of （）.
A.10
B.7
C.4
D.1 -
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If over a period of weeks the air-box pressure of a turbo-charged, diesel engine, operating at full load, appears to be dropping off, the cause can be （）.
A.open air-box drains
B.loss of cooling water to the diffuser
C.gradual fouling of the air filters
D.improperly timed exhaust valves
