The correct option is C It
Option C: Pronouns refer to nouns that have been mentioned before.
The given passage states the uses of wood in the first few sentences.
In the given sentence, it is mentioned that 'he burns wood to cook food for himself'. Since 'wood' has already been mentioned before, we use a pronoun in its place.
'It' is a pronoun that refers to objects like wood. Hence this is a suitable option and C is correct.
Option A: 'Wood' will not be used again to avoid repetition.
Option B: 'Him' refers to a person. A person cannot be burned to cook food. The meaning is unclear: he burns him to cook food.
Option D: 'Them' also refers to people whereas here 'wood' is burned'.
Hence options A, B and D are incorrect.