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

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