Analyze the relationship between 'Syriza' and 'Alexis Tsipras' within the context of the input sentence.
Options: chairperson, distributed by, product/material produced, chief executive officer

Already, Prime Minister Alexis Tsipras is struggling to contain a rebellion in his leftwing Syriza party that made his government dependent on votes from pro-European opposition parties to get the tough bailout terms approved in parliament.
chairperson