Utilize the input text as a context reference, choose the right relationship between 'Banamex' and 'Citigroup' from the options.
Options: parent organization, publisher, operator, stock exchange

Citigroup Inc. on Wednesday confirmed that it will close Banamex USA, a small unit doing business across the U.S.-Mexico border, and agreed to pay $140 million to regulators who said the unit hadn’t done enough to protect itself from money launderers.
operator