Utilize the input text as a context reference, choose the right relationship between Walgreens and Stefano Pessina 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.

Stefano Pessina is to become permanent chief executive of Walgreens Boots Alliance, the retail pharmacy giant announced on Thursday.

Answer: chief_executive_officer