The correct answer is B Subduction. Subduction is the process by which an oceanic plate gets dragged under another plate and is eventually destroyed in the mantle. Subduction occurs at convergent margins where two oceanic plates collide or an oceanic and Continental plate collide. Oceanic crust is made of mainly of silica and magnesium which is heavier or denser than continental crust which is composed mainly of silica and aluminium. The subducting plate melts producing excess magma giving rise to volcanoes along these margins.
Why might a post classical civilization want to conquer Egypt and the Nile River Valley? It's fertile land provided the foundation for the first human civilizations and its access to the Persian Gulf and location between Europe, Asia, and Africa made it a center of trade.
