Utilize the input text as a context reference, choose the right relationship between grocery and Walmart 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.

Measured by revenue, Walmart is the largest company in the world and the largest grocery retailer in the United States.

Answer: operator