What is the relationship between Tim Cook 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.

Sept 18 Apple Inc is stepping up aid to the thousands of migrants that are streaming into Europe from war-torn countries, Chief Executive Officer Tim Cook told employees in an internal message on Friday.

Answer: position_held