The chief source(s) of oils used to make soap is/are:
The chief source(s) of oils used to make soap is/are plants and animals. This is because soaps are a combination of animal fats or plant oils. They are used to clean and treat the skin and clean utensils and clothes. The first of soaps were made from the remains of a goat and ash of wood. A substance similar to foam formed which hardened once it cooled.
Hence, option C is correct.