Utilize the input text as a context reference, choose the right relationship between 'AmEx' and 'American Express' from the options.
Options: owned by, employer, operator, owner of

Sam’s Clubs to Accept AmEx Cards Earlier this year, retailer Costco cut ties with American Express after 16-year relationship By lisa.beilfuss@wsj.com Updated Sept. 10, 2015 5:41 p.m.
operator