Diesel engines obtain combustion air through turbo chargers，blowers，or（）.

A.they are more heavily built
B.the fuel used is less volatile
C.they can be easily reversed
D.they operate at a lower speed

A.Oil level
B.Flow of cooling water
C.Exhaust discharge
D.All of the above

A.Four-stroke
B.Two-stroke
C.Electronic ignition
D.Forced exhaust