Which one of the following types of plains is not formed by the action of the riven?

Loess plains is not formed by the action of the river. Loess is a sedimentary deposit of mineral particles which are finer than sand but coarser than dust or clay, deposited by the wind. Loess is a type of silt which forms fertile topsoil in some parts of the world. Loess deposits are usually a few meters thick. The soil has few clay particles to hold it together.