Option b is the correct answer. The first double dome structure built by Sikandar Lodi was the tomb of his father, Bahlul Lodi, in Delhi. A double dome is built of two layers. There is one layer inside which provides ceiling to the interior of the building. The other layer is the outer one which crowns the buildings. The attempts in the direction of Double Dome continued with tomb of Taj Khan (1501) and the tomb of Sikandar Lodi (1518), both in Delhi. The tomb of Sher Shah in Sasaram, Bihar, stands as an exemplar of Indo-Islamic architecture. Designed by Mir Muhammad Aliwal Khan, it was constructed between 1540 and 1545. The tomb rests on a square stone plinth, encircled by an artificial lake. It boasts an octagonal main structure crowned by a 22 -meter dome, accompanied by ornamental domed kiosks. The Tomb of Ghiyas ud din Balban in Mehrauli, Delhi, is historically significant for introducing the first true Islamic arch in India. Although its original dome is lost, it marks the development of Indo-Islamic architecture. Gol Gumbaz is a 17th-century mausoleum located in Bijapur, Karnataka, India. It houses the remains of Mohammad Adil Shah, the seventh sultan of the Adil Shahi dynasty.