Given the input sentence, please extract the subject and object containing a certain relation in the sentence according to the following relation types, in the format of "relation1: word1, word2; relation2: word3, word4". Relations include: product/material produced; manufacturer; distributed by; industry; position held; original broadcaster; owned by; founded by; distribution format; headquarters location; stock exchange; currency; parent organization; chief executive officer; director/manager; owner of; operator; member of; employer; chairperson; platform; subsidiary; legal form; publisher; developer; brand; business division; location of formation; creator.

Shares of United over the past five years have generated about half the return of rival Delta Air Lines , and analysts have worried the company is falling behind once-bankrupt American Airlines Group as that company integrates its merger with US Airways Group .
parent_organization: US Airways, American Airlines Group; subsidiary: American Airlines Group, US Airways; owner_of: American Airlines Group, US Airways; owned_by: US Airways, American Airlines Group