Which of the fire extinguishing agents listed is the safest to use when combating a class C fire?（）

A.More than six short blasts and one long blast on the whistle
B.Continuous blast of the ships whistle for a period of not less than 10 seconds supplemented by the same signal on the general alarm
C.Three short blasts of the whistle supplemented by the same signal on the general alarm
D.More than six short blasts and one long blast on the whistle supplemented by the same signal on the general alarm

A.mechanical foam
B.chemical foam
C.carbon dioxide
D.soda acid

A.Dry chemical
B.Halon
C.Low velocity fog
D.Steam