Option a is the correct answer. Nagarjuna was a 2nd-century Indian Buddhist philosopher who is considered to be one of the founders of Mahayana Buddhism. He is also credited with introducing the Madhyamaka school of Mahayana Buddhism, which is based on the doctrine of emptiness, or sunyata. The doctrine of emptiness states that all phenomena are empty of inherent existence. This means that they do not have any independent reality of their own. They are simply dependently originated, which means that they arise in dependence on other factors.