Analyze the relationship between 'Syriza' and 'ATHENS' within the context of the input sentence.
Options: currency, creator, headquarters location, manufacturer

ATHENS (Reuters) - Greek Prime Minister Alexis Tsipras, struggling to contain a revolt in his left-wing Syriza party, said on Wednesday that his government would not implement reform measures beyond those agreed with lenders at a euro zone summit this month.
headquarters location