Utilize the input text as a context reference, choose the right relationship between 'Walgreens' and 'Walgreens Boots Alliance' from the options.
Options: stock exchange, business division, parent organization, currency

Walgreen is part of Walgreens Boots Alliance Inc, and this year sold a majority stake in Trinity's parent Walgreens Infusion Services to private equity firm Madison Dearborn Partners.
parent organization