单项选择题

The pH value of water in a diesel engine closed cooling water system should be maintained between （）.

A.60 to75
B.80 to 95
C.100 to 115
D.120 to 135

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Indirect cooling of fuel injector nozzle holders for diesel engines is accomplished primarily by （）.

A.heat conduction into the injected fuel oil
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C.water circulation through passages in the holder
D.fuel oil circulation through passages in the holder

单项选择题

In a diesel engine cooling water system, a pH of 60 indicates a/an （）.

A.slightly acidic condition
B.slightly alkaline condition
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Which of the following statements concerning fire-tube boilers is correct?（）

A.Combustion gases flow through the tubes
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C.Combustion occurs in the tubes
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