The correct answer is (a) Amir Khusrau.
Amir Khusrau was a 13th-14th-century Indian poet, musician, and scholar who was born in Delhi. He is considered to be one of the greatest poets of the Delhi Sultanate period and is known for his versatility in both Persian and Hindi. He is also credited with introducing the qawwali form of music to India.
Amir Khusrau witnessed the reign of seven Sultans of Delhi: Qutbuddin Aibak, Iltutmish, Razia Sultan, Alauddin Khalji, Muhammad bin Tughluq, Firuz Shah Tughluq, and Ghiyasuddin Tughluq. He served as a court poet to several of these Sultans and wrote extensively about their reigns.
Shaikh Nizamuddin Aulia (b) and Khwaja Moinuddin Chisti (c) were both Sufi saints who lived in the 13th century. They were not court poets and did not witness the reign of any Sultans.
(d) None of the above is also incorrect because Amir Khusrau did witness the reign of seven Sultans of Delhi.