In relation to cargo gear，what does SWL mean?（）.

A.crow bar
B.device to force a water tight door against the frame
C.heavy steel beam
D.wedge

A.that the fuel valve is open
B.if the air supply system is open
C.if the water sprinkler system is open
D.if the limit switch is on

A.a defective ignition system
B.low lube oil level
C.weak valve springs
D.too heavy a load