What is the relationship between Mary Barra and chief executive officer 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.

GM chief executive officer Mary Barra told reporters in June that she would not negotiate with the UAW in public and preferred to keep any discussions behind closed doors -- a policy both sides have adhered to since talks began last month.
position_held