In the context of the input sentence, determine the relationship between 'Syriza' and 'ATHENS'.
Options: headquarters location, industry, parent organization, legal form

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