Step 1: Recall Sanchi's history: The Great Stupa at Sanchi (Madhya Pradesh) was originally commissioned by Emperor Ashoka in the 3rd century BCE to house relics of the Buddha.
Step 2: Confirm the association: Sanchi remained a major Buddhist site through the Shunga and Satavahana periods, famous for its toranas (gateways) depicting Jataka stories.
Final Answer: Buddhism – option (D).