Answer:
He wrote mostly about the Midwest and its people.
Step-by-step explanation:
Regionalism is when a writer wrote mostly about a certain geographical region, about the landscape, culture, and any features of a particular region. This means that the writer focuses on writing about that particular region and localized presentation.
Carl Sandburg can be described as a regional poet because his works mostly concern the Midwest area. His major works include "The Chicago Race Riots (1919), Poems of the Midwest (1946), Chicago Poems (1916), and Cornhuskers (1918)", among others. His pattern of focusing on the people and culture of the Midwest made him a regional poet.
Thus, the correct answer is the third option.