What is the relationship between eurozone and euro 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.

Greece's fellow eurozone members have widely rounded on Mr Tsipras for backing a 'No' vote, warning that he must choose between keeping the euro or returning to the drachma.

Answer: currency