The sub-branch of metaphysics that deals with the nature of existence itself is:

a. Cosmological

b. Anthropological

c. Ontological

d. Theological

C. Ontological

Explanation:

Metaphysics itself is a branch of philosophy that advocates beyond physical or abstract concepts and ontology is a sub-branch of metaphysics dealing with the nature of being or existence. It focuses on the concepts related to human existence and their relations. It questions the objective reality and attempts to find the meanings of being. for example, Plato and Aristotle both proposed their ontological theories, the former gave the distinction between the true reality and illusion while the latter provided the existence of ten different kinds of beings.