What is the relationship between Southwest Airlines and Dallas in the context of the input sentence. Choose an answer from: 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.

"We have not grown Southwest Airlines in three or four years," but now "we have opportunities to grow like we haven't had in years," CEO Gary Kelly said, citing Dallas and Houston.

Answer: location_of_formation