Correct Answer:
C. Khairpur
The archaeological site of Kot Diji, which represents a significant pre-Harappan phase of the Indus Valley Civilization, is located in the Khairpur District of Sindh, Pakistan. This site provides crucial insights into the early development of urban centers and cultural practices before the mature Harappan period. While Sukkur, Larkana, and Dadu are also districts in the Sindh province, Khairpur is the specific district where the Kot Diji civilization site is found, making it the correct answer.