The correct answer is A) the Upanishads.
The Upanishads are a set of sacred Indian texts that contain central philosophical and spiritual concepts of the Hindu tradition. They were written between the 7th century BE and 300 CE by gurus to explain to common people the ideas of Brahman, the highest universal principles, and Atman, the soul. They also deal with philosophical content and ethical precepts like non-violence, charity, and compassion.