Answer:
C. were formed from plants which did not have time to decay
Step-by-step explanation:
Coal beds are formed from plants which did not have time to decay. They usually form in an anoxic environment where oxygen is lacking and there is abundant plant matter.
The best place where coal beds can form is in a swamp.
Rapid burial of the plant matter without reacting with oxygen maintains the carbon content and the chemical energy they hound.