The preferred agent used in fighting a helicopter crash fire is（）.

A.45°upward
B.vertically upward
C.vertically downward
D.all of the above

A.all emergency signals
B.instructions for lowering the survival craft
C.the time each weekly drill will be held
D.work schedule

A.driving wooden plugs into the vents
B.closing the lids on the vents
C.plugging the scuppers
D.plugging the sounding pipes