Refer to the input text as context and select the correct relationship between 'Syriza' and 'ATHENS' from the available options.
Options: legal form, product/material produced, headquarters location, operator

ATHENS - 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