单项选择题
A Kort nozzle is a(n)（）.
A.hollow tube surrounding the propeller used to improve thrust B.nozzle attached to a firefighting hose C.intake valve on a diesel engine D.piston cylinder on a diesel engine
单项选择题 A hydraulic accumulator aboard a ship is designed to（）.
单项选择题 A fuel-air mixture below the lower explosive limit is too（）.
