What is the relationship between 'grocery' and 'Walmart' in the context of the input sentence.
Options: operator, director/manager, manufacturer, currency

"As competitors like Kroger, Publix, H-E-B, Jewel-Osco and others have invested in evolving customer lifestyle trends – by broadening organic and fresh offerings – and in improving customer service, the gap between both comp-store sales growth and customer satisfaction at Walmart U.S. grocery and supermarket competitors continues to widen," Hood writes.
operator