Final answer:
The best example of a functional region is the Dallas/Ft. Worth Metroplex.
Step-by-step explanation:
A functional region is a region defined by a practical function within a given area. The best example of a functional region from the given options is the Dallas/Ft. Worth Metroplex.
The Dallas/Ft. Worth Metroplex is a region in Texas that serves as a major economic, cultural, and transportation hub. It has established boundaries for the limits of the area to which it provides services, such as transportation, commerce, and entertainment. The region functions together in various aspects, making it a prime example of a functional region.