Combustible gas indicators measure the presence of combustible gas as a percentage of the（）.

A.cooling
B.smothering
C.chemical action
D.All of the above

A.a tug comes alongside while the tanker is loading grade D and E cargoes
B.a large，fresh oil spill is discovered immediately adjacent to the side of the tanker
C.there is an electrical storm in the vicinity
D.there is a fire on the dock or on a nearby vessel

A.fixed foam systems to be ineffective
B.faster cooling of the fire
C.the accumulation of explosive gases
D.the fire to spread through the ventilation system