The relics of Sariputra and Mahamoggallana, the disciples of the Buddha, are said to have been placed in:

Correct option is D

The relics of Sariputra and Mahamoggallana, the two chief disciples of the Buddha, are said to have been placed in Sanchi Stupa No. 3.

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The Sanchi Stupas are a complex of Buddhist monuments in Madhya Pradesh, India.

Stupa No. 1 (The Great Stupa) is the largest and oldest structure, believed to contain relics of the Buddha himself.
Stupa No. 3 is a smaller stupa located near the Great Stupa. Excavations conducted by Sir Alexander Cunningham in 1851 discovered a stone box inside this stupa containing two steatite caskets.

The inscriptions on these caskets identified them as containing the relics of Sariputra (Sariputrasa) and Mahamoggallana (Mahamogalanasa).