The great plains are also referred to

a. marshes c. interior plains b. lowlands d. plateaus

[b is incorrect]

The Great Plains are also referred to as interior plains.

Explanation:

The Great Plains form a huge part of the "interior plains" that stretch from Canada to the central United States. These plains are home to bunchgrass steppes, shortgrass and tallgrass prairies, and a few other less-known species of stunted shrubs. The black and brown fertile soils favor the cultivation of grain plants. These plains are thus known for their production of wheat and other grains.

Ba rock that formed 1,400 million years ago!

Ashould be answer.