What is the relationship between 'SkyMiles' and 'Delta Air Lines' in the context of the input sentence.
Options: operator, developer, stock exchange, manufacturer

Delta Air Lines will radically change its SkyMiles frequent flier program next year, becoming the first of the "big three" U.S. airlines to ditch a fixed miles-for-a-free-flight system in favor of a supply-and-demand scheme that may require more mileage points to fly on more popular routes.
operator