A.at high speed and full loadB.at low speed and part lo……

单项选择题A common rail engine has only one or two high pressure pumps in operation at the same（）time, and the injection into each cylinder.

A.can’t be controlled very precisely
B.can’t be controlled as flexibly as the separate pump system
C.can be controlled as flexibly as the separate pump system
D.can be controlled more precisely and flexibly

单项选择题（）uses one or two high pressure pumps for all the cylinders with one more standby, while（）have a separate high-pressure pump for each cylinder.

A.A common rail engine；conventional engines
B.A conventional engine；common rail engines
C.A marine diesel engine；most other engines
D.A two-stroke engine；four-stroke engines

单项选择题In a common rail engine, the fuel is injected into cylinders（）

A.by injection pumps
B.at a time decided by the injection pump timing
C.by a signal opening the magnetic valves
D.at a time decided by the cam directly

单项选择题In common rail engines, the fuel is（） before is injected into the cylinders.

A.stored in a common fuel line
B.pumped by the injection pump
C.at low pressure
D.already atomized

单项选择题In conventional systems, the injection pressure（）, while it’s（）in common rail diesel engines.

A.fluctuates with the engine speed to some extent, independent of the engine speed
B.keeps constant at all engine speed, dependent on the engine speed to some extent
C.keeps constant at all engine speed, independent of the engine speed
D.is decided by the engine speed, constant at all engine speed