Concept:Glacial erosion by two back-to-back corries creates a sharp, knife-edged ridge.
Explanation:A corrie is a bowl-shaped hollow carved out by glacial ice.
When two corries develop on opposite sides of the same mountain, they erode headward into the slope.
The rock wall between them is gradually worn down into a narrow, jagged crest.
This sharp, knife-edged ridge is called an arete.
A pyramidal peak requires three or more corries, not just two.
Answer:D. Arete