Concept:Pediplains are extensive flat surfaces formed in dry regions as mountain slopes retreat due to weathering.
Explanation:In arid and semi-arid areas, mechanical weathering attacks the sides of mountains.
Over time, the slopes gradually wear back and retreat.
This process leaves behind broad, gently sloping rocky plains at the foot of the mountains.
These plains eventually join to form a large erosion surface called a pediplain.
Outwash plains are formed by glacial meltwater, while alluvial plains are formed by river deposits.
Therefore, plains produced by the retreat of mountain slopes in dry regions are pediplains.
Answer:C. Pediplains