Answer: Option (D)
Explanation: In order to form coal, two processes might be undergone and they are as follows-
- Peatification- It is the process by which the remains of trees and plants undergoes partial decomposition in a swampy type of environment, conserving organic matter. It is the first stage of coal formation.
- Coalification- It is the process of complete transformation of the dead remains of plants and trees into coal.
Thus the correct answer is option (D).
