Concept:Fertile plains are usually formed by the deposition of nutrient-rich materials, while erosional plains are not.
Explanation:Loess plains consist of wind-blown silt that is very fertile.
Alluvial plains are built from river-deposited sediments rich in minerals and plant nutrients.
Flood plains receive fresh layers of alluvium during flooding, which keeps their soil fertile.
Erosional plains, however, are formed by the wearing away of the land surface, often exposing less fertile subsoil.
Therefore, erosional plains are the only type that is not fertile.
Answer:C. erosional plains