單項選擇題In order to keep the oil film on the cylinder liner during the running-in period, the piston rings are slightly rounded（）

A.on both the external and internal top edges
B.on both the external top and bottom edges
C.on both the external and internal bottom edges
D.on all the four edges


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1.單項選擇題In some type of two-stroke engines, besides some small holes for（）, starting valve, safety valve, indicator cock, and central opening in each cylinder cover for mounting the（）

A.fuel valves；exhaust valve
B.exhaust valves；inlet valve
C.fuel valves；inlet valve
D.exhaust valves；fuel valve

2.單項選擇題In a two-stroke engine, there are always a series of openings known as （）, and in some circumstances, there are also openings known as （）, in the part of the cylinder liner.

A.scavenging air ports；exhaust ports
B.inlet ports；scavenging air ports
C.scavenging air ports；inlet ports
D.exhaust ports；inlet ports

4.單項選擇題（）is the main reason that reduces the power advantage of a two-stroke engine over a same size four-stroke one to about（）

A.Inefficient scavenging；twice
B.Inefficient scavenging；1~8 times
C.Fewer strokes in a circle；twice
D.Fewer strokes in a circle；1~8 times

5.單項選擇題In a diesel engine, when the fuel is injected into the cylinder,（）

A.the piston is just coming upward from the bottom dead center
B.the piston has moved about one-fifth of the way up
C.the piston has moved most of the way up and almost reached the TDC
D.the piston has just past the TDC