The correct answer is: C. Pali
Pali is a Middle Indo-Aryan language that was used to write the Theravada Buddhist canon. It is a close relative of Sanskrit, but it is not the same language. Pali is a much simpler language than Sanskrit, and it is easier to learn.
Brahmi is an ancient writing system that was used to write many different languages, including Sanskrit, Pali, and Prakrit. It is not a specific language in itself.
Sanskrit is an ancient Indo-Aryan language that was used to write many different religious texts, including the Vedas and the Upanishads. It is a very complex language, and it is difficult to learn.
Magadhi is a Middle Indo-Aryan language that was spoken in the region of Magadha in India. It is the language in which the Buddha preached his sermons.
The original Buddhist religious texts were written in Pali. Pali is a Middle Indo-Aryan language that is closely related to Sanskrit. It is the language in which the Buddha preached his sermons, and it is the language in which the Theravada Buddhist canon is written. Pali is a relatively simple language, and it is easier to learn than Sanskrit.