Explanation:

The Qutub Minar is a UNESCO World Heritage Site in Delhi, India, an iconic example of Indo-Islamic architecture, whose construction spanned several reigns. \nA. Qutubuddin Aibak: Qutubuddin Aibak, the founder of the Mamluk dynasty and the first Sultan of Delhi, initiated the construction of the Qutub Minar in 1192 CE. He managed to complete only the basement story of the minaret before his death in 1210 CE. Therefore, he started it but did not complete it. \nB. Iltutmish: This is the correct answer. Iltutmish, Qutubuddin Aibak's successor and son-in-law, is widely credited with completing the Qutub Minar. He added three more stories to the structure, bringing it to its full height (at that time) and largely finishing the construction. The minar was completed during his reign (1211-1236 CE). \nC. Firoz Shah Tughlaq: Firoz Shah Tughlaq, a later Sultan from the Tughlaq dynasty (reigned 1351-1388 CE), was responsible for repairing the Qutub Minar after it was damaged by lightning in 1368 CE. He replaced the damaged top story with two new stories, made of white marble and red sandstone, giving the minar its present appearance. He contributed to its restoration and modification, not its initial completion. \nD. Alauddin Khilji: Alauddin Khilji, a powerful ruler of the Khilji dynasty (reigned 1296-1316 CE), made significant additions to the Qutub complex, such as the Alai Darwaza (the southern gate of the Quwwat-ul-Islam Mosque) and attempted to build a minar even taller than Qutub Minar (the Alai Minar), but he was not involved in the completion of the Qutub Minar itself.