The correct option is B Philosophy
Upanishads deal with philosophical aspect of Hinduism, and is central to various philosophical traditions of India. It covers ethics, cocpet of Brahman (God), soul etc. The Upanishads are referred as "Vedanta" or the last chapter of Vedas and explain the meaning of Vedas or the purpose for which Vedas were written. They have been instrumental in spreading Indian philosophical traditions to all over the world.