Final answer:
The correct answer is option D. Narmer.
Step-by-step explanation:
The unification of Upper and Lower Egypt into a single kingdom is a significant event in ancient Egyptian history, occurring around 3150 BCE. While there has been some debate over the identity of the ruler responsible for this unification, the majority of evidence points to a king named Narmer.
This historic figure is often equated with Menes, a king who also has been credited with the unification. In any case, scholars widely consider them to be the same person. This unification marked the beginning of the Old Kingdom period and set the stage for Egypt's rise as a powerful and culturally rich civilization.
To answer the student's question directly: King Narmer (D.) is traditionally credited with uniting ancient Egypt.