What is the relationship between 'Rubicon Project' and 'LOS ANGELES' in the context of the input sentence.
Options: employer, publisher, creator, headquarters location

LOS ANGELES & LONDON--(BUSINESSWIRE)-- Launch of Argentina and Hungary Advertising Co-Ops Expands Rubicon Project Leadership Role as The Exclusive Publisher Co-operative Marketplace Serving More Than 290 Premium Publishers Globally
headquarters location