Question

upwards convection of asthenosphere material occurs most frequently beneath:
ocean trenches
midocean ridges
continental mountain ranges
abyssal plains

Explanation:

To solve this, we analyze each option:

• Ocean trenches: Associated with subduction (material sinks), not upward convection.
• Midocean ridges: Form at divergent plate boundaries where asthenosphere material rises (convection upwells) to create new oceanic crust.
• Continental mountain ranges: Often from continental - continental convergence; less about asthenosphere upward convection at their base compared to mid - ocean ridges.
• Abyssal plains: Flat ocean floors, no significant upward asthenosphere convection here.

So the correct option is the one related to divergent boundaries with upward convection of asthenosphere material.

Answer:

B. midocean ridges