The best statement summarizing the difference between formal and functional regions is:
"A functional region is an area characterized by one or more activities occurring in that area, whose boundary is usually more loosely defined. A formal region is an area on Earth’s surface defined by relatively unchanging cultural or physical traits, often associated with a formal boundary."
This captures the key distinctions: functional regions are defined by activities and have flexible boundaries, while formal regions are defined by specific, unchanging characteristics and often have clearly defined boundaries.