Utilize the input text as a context reference, choose the right relationship between Donald Tusk and President of the European Council from the options. Options: 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