Purana Qila at Delhi was built by

Answer: Option B

Sher Shah's fort or the Purana Qila. It stands on the ancient site, known as 'Indraprastha', associated with the Hindu epic Mahabharata. He was temporarily deposed by Sher Shah Sur (r. 1540-45), who completed the fortress walls and built two important structures, that were used by Humayun when he took back the city.