Question

What is one way a plain can form

Answer 1

Plains form in many different ways. Some plains form as ice and water erodes, or wears away, the dirt and rock on higher land. Water and ice carry the bits of dirt, rock, and other material, called sediment, down hillsides to be deposited elsewhere.
Volcanic activity can also form plains.
Hope this helps:)

Answer 2

The plains can be formed in several ways, one of them is given by the accumulation of Sediments that have been attracted by the wind or the sea over the years, although it can also be due to the accumulation of Lava that has been deposited forming several layers of it and resulting in a large area of land.