Utilize the input text as a context reference, choose the right relationship between MileagePlus and United Airlines from the options. Options: product/material produced, manufacturer, distributed by, industry, position held, original broadcaster, owned by, founded by, distribution format, headquarters location, stock exchange, currency, parent organization, chief executive officer, director/manager, owner of, operator, member of, employer, chairperson, platform, subsidiary, legal form, publisher, developer, brand, business division, location of formation, creator.

The United MileagePlus Club Card is the elite version of the Explorer card and offers exclusive travel benefits for those who travel with United Airlines frequently.

Answer: operator