What is the relationship between Donald Tusk and President of the European Council in the context of the input sentence. Choose an answer from: product/material produced; manufacturer; distributed by; industry; position held; original broadcaster; owned by; founded by; distribution format; headquarters location; stock exchange; currency; parent organization; chief executive officer; director/manager; owner of; operator; member of; employer; chairperson; platform; subsidiary; legal form; publisher; developer; brand; business division; location of formation; creator.

LUXEMBOURG, July 9 National parliaments should be convinced to vote in favour of helping Greece if European leaders can reach a good agreement on Sunday, President of the European Council Donald Tusk said, adding that a deal on debt should be part of the agreement.

Answer: position_held