What is the relationship between Stock market and stock exchange 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.

Stock market officials and historians calculate that the Athens stock exchange has been forced to cease trading for at least a day on 14 other occasions since the bourse was founded and started trading in 1876.

Answer: operator