Utilize the input text as a context reference, choose the right relationship between 'Syriza' and 'ATHENS' from the options.
Options: legal form, parent organization, headquarters location, industry

ATHENS (Reuters) - The leftist Syriza party of former Prime Minister Alexis Tsipras will challenge Greece's creditors on unresolved aspects of the nation's bailout but implement unpopular reforms it has already agreed, it said on Sunday.
headquarters location