Final answer:
The described civilization that relied on the Nile River for agriculture and trade, known for its sophisticated irrigation systems and wealth from trade, is undoubtedly Egypt.
Step-by-step explanation:
The passage given describes the early river valley civilization which relied heavily on the Nile River for irrigation, agriculture, and trade, becoming wealthy and developed in the process. The detailed description of irrigation systems, agricultural richness, and the significant role of trade between central and northern African civilizations points to the answer as Egypt. This civilization was distinctive for its predictable flooding of the Nile, which contributed to its soil's fertility, its ability to sustain structured, urbanized growth, and its location which became a hub for trade. Through the use of sophisticated irrigation and the Nile's dependable flooding patterns, Egypt prospered, with its many cities and monuments along the river's banks, including the Giza pyramids and the Sphinx. Trade, coupled with agricultural surpluses, played a crucial role in its economic wealth. All of these factors confirm that the civilization described is indeed Egypt, not Sumeria, Nubia, or Akkadia.