What would be an example of a formal region? A-the rust belt in the united states
B-“back home”
C-the commuter bus loop in dallas tx
D-the subway system in new york city

The rust belt of the united states would be a formal area do to the whole area all being swing states, or that they were all specialized in iron and steel production in before the 1970's.

Explanation:

A formal region is an area inhabited by people who have one or more characteristics in common. Shared characteristics may be a common language, economic activities, such as a particular crop production, or physical characteristics, such as the climate of an area. Some formal regions have distinct boundaries which make them easy to identify, such as counties or states. Examples of formal regions are Europe, Africa, United States, and Canada.