Concept:Human population tends to concentrate where natural resources support reliable food production and settlement.
Explanation:The Nile Valley is surrounded by desert, so the regional climate alone is not the main reason for its dense population.
The annual flooding of the River Nile deposits rich alluvial soil on its banks.
This alluvial soil is very fertile and supports intensive crop cultivation throughout the year.
High agricultural productivity can feed a very large number of people within a small area.
As a result, farming communities grow and permanent settlements become densely packed along the valley.
Seasonal migration from Europe during winter does not create a permanent high population density.
The Nile Valley is also not known for numerous oil fields; petroleum deposits are mostly located in other parts of Egypt.
Therefore, it is the presence of rich alluvial soil that best explains the high population density in the Nile Valley.
Answer:C. Presence of rich alluvial soil