CO₂ cylinders equipped with pressure actuated discharge heads will discharge automatically when（）.

A.the discharge valve is open

B.the control box glass is broken

C.pressure from the control cylinders is detected

D.the control cylinders have been completely discharged

航程在8000公里以上的旅客机称为（）

A、短程客机

B、中程客机

C、远程客机

D、中短程客机