單項選擇題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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1.單項選擇題Indirect cooling of fuel injector nozzle holders for diesel engines is accomplished primarily by （）.

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

2.單項選擇題In a diesel engine cooling water system, a pH of 60 indicates a/an （）.

A.slightly acidic condition
B.slightly alkaline condition
C.overtreatment of water
D.neutral condition of water

3.單項選擇題Which of the following statements concerning fire-tube boilers is correct?（）

A.Combustion gases flow through the tubes
B.Flames impinge on the tubes
C.Combustion occurs in the tubes
D.Water flows through the tubes

4.單項選擇題A diesel engine cooling water system with a pH factor of 30 indicates a condition of （）.

A.slight acidity
B.slight alkalinity
C.excessive alkalinity
D.excessive acidity

5.單項選擇題Fuel injectors used in heavy fuel oil systems are usually provided with cooling to reduce（）.

A.cold corrosion of the nozzles
B.fuel viscosity for better atomization
C.carbon accumulation on the nozzles
D.fuel detonation in the cylinders