What type of combustion is represented by:

(a) Burning of white phosphorus in air at room temperature is a spontaneous combustion. The type of combustion in which a material suddenly bursts into flames, without the application of any apparent cause is called spontaneous combustion.
(b) Burning of LPG is combustion in which a substance burns rapidly and produces heat and light with the help of external heat.
(c) Ignition of a cracker is a combustion in which a substance burns suddenly and produces heat, light and sound with the help of heat or pressure.
(d) Burning of coal dust in a coalmine is a spontaneous combustion. The type of combustion in which a material suddenly bursts into flames, without the application of any apparent cause is called spontaneous combustion.