What is the relationship between Petrobras and RIO DE JANEIRO 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.

RIO DE JANEIRO Aug 28 Brazilian Senator Jose Serra said on Friday he expects a vote on changing the country's oil law to ease demands on state-run firm Petrobras and reduce local content rules to take place in September.

Answer: headquarters_location