What is the relationship between 'Syriza' and 'Alexis Tsipras' in the context of the input sentence.
Options: chairperson, distributed by, legal form, subsidiary

Greek Prime Minister Alexis Tsipras is also under pressure from many in his radical left Syriza party who say the new accord will pile further austerity on a weakened economy and goes against the party's campaign pledges.
chairperson