单选题The opening of an exhaust valve on a modem, large, low-speed, main propulsion diesel engine may be actuated by （）.Adirect action of cam shaftBcompressed air pressureChydraulic “push rods”Ddirect action of the main piston moving down
单选题
The opening of an exhaust valve on a modem, large, low-speed, main propulsion diesel engine may be actuated by （）.
A
direct action of cam shaft
B
compressed air pressure
C
hydraulic “push rods”
D
direct action of the main piston moving down
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