The correct option is A Sanchi
The "Great Stupa" at Sanchi is the oldest structure and was originally commissioned by the emperor Ashoka the Great of the Maurya Empire in the 3rd century BCE. Hence, Option A is correct. Bharhut stupa was built at around 100 BCE. Amaravati stupa was built at about 250 BCE. The original stupa was renovated by the Ikshvaku princess Chamtisiri in the 3rd century AD when Ayaka-pillars of stone were erected. Hence, these options are incorrect.