What is the relationship between Opera Australia and Sydney 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.

Opera Australia -- which uses the Sydney Opera House for it's performances -- encourages selfies during performance intervals, however, only at arms length and not with a selfie stick.

Answer: headquarters_location