About the jacket water, that of the auxiliary engines usually（） is circulated by pumps, and the main engine usually （）

单项选择题The cooling system（） needs least maintenance work for in this kind of system（）

A.open；the minimum components
B.open；the high cooling efficiency
C.central；there are more coolers and a extra set of pumps
D.central；there is only one component contacts seawater

单项选择题An alarm device inserted between the deaerating tank and the expansion tank can notify the on-watching crew that （）

A.the expansion tank is lack of water
B.the expansion tank is over flowing
C.there is something wrong with the cooling system
D.there is something wrong with the engine

单项选择题As an alternative to the conventional seawater cooling system, is based on principles about cooler locations, （）flow control and preheating, but with a central cooler and one additional set of pumps（）.

A.the central cooling system, different
B.the central cooling system, the same
C.the open cooling system, different
D.the open cooling system, the same

单项选择题（）is harmful for fuel pumps, fuel valves, cylinder liner, exhaust valve seats, and the turbocharger blades as well.

A.Bad combustion of the fuel
B.Bad atomization of the fuel
C.Liquid contaminants
D.Solid contaminants

单项选择题The booster pump, which supplies diesel oil to（） , should have a possibility of being powered by compressed air or by emergency power.

A.the main engines
B.the auxiliary engines
C.the emergency generator engine
D.the auxiliary engines and the main engine(s)