Which of the following is a non-religious source about the ancient history of Bihar?

The correct answer is D. Kalpsutra.

A. Gargi Samhita is a Hindu religious text.
B. Abhidhamma Pitaka is a Buddhist religious text.
C. Rigveda is a Hindu religious text.

The Kalpsutra is a Jain religious text. It is a collection of stories and teachings that are said to have been given by the 24th Tirthankara, Mahavira. The Kalpsutra is an important source of information about Jain history and culture.

The other three options are all Hindu religious texts. The Rigveda is the oldest of the four Vedas, which are the foundational texts of Hinduism. The Abhidhamma Pitaka is the third part of the Tipitaka, which is the Buddhist canon. The Gargi Samhita is a collection of hymns and verses that are attributed to the sage Gargi.