Option a is the correct answer. Qila-i-Kuhna Masjid, also known as the "Mosque of the Old Fort," was constructed by Sher Shah Suri in 1541 as a congregational mosque. It stands as a remarkable structure alongside Sher Mandal as the only two surviving remnants of Delhi's Purana Qila, a project initiated by Sher Shah but ultimately completed during Humayun's reign. The mosque boasts a 5 bay structure with 3 domes, showcasing architectural influences from the earlier periods of Sher Shah Suri, as well as the Sayyids and the Lodis under Humayun's direction. Important Tips Facts about significant monuments: In 1408 A.D., Ibrahim Shah Sharki constructed the Atala Masjid, which later became the model for other mosques in Jaunpur. The Baradarwazi or Bara Sona Masjid, renowned as the large golden mosque, was built by Sultan Nusrat Shah in 1526 and remains the largest standing building in Gaur. As for the Quwwat-ul-Islam Mosque, it was sponsored by Qutb-ud-din Aibak, the founder of the Mamiuk dynasty, and stands as the earliest extant mosque built by the Delhi Sultans.