Explanation:

- Bharatanatyam is a classical dance form from South India.

- It traditionally delves into religious themes and spiritual ideas.

- ?? Option 2: Shaivism is the correct answer. Bharatanatyam often reflects the worship of Shiva, a major deity in Shaivism.

- Option 1: Sufism is related to mystical Islamic beliefs, prevalent more in West and Central Asia. It is not typically expressed through Bharatanatyam.

- Option 3: Buddhism is a major religion originating from India, but not specifically expressed in Bharatanatyam.

- Option 4: Jainism is an ancient Indian religion, but it is not a prominent theme in Bharatanatyam.