Zhōngguó shì Ōuméng zuì zhòngyào de hézuò huǒbàn zhī yī.
China is one of the EU's most important cooperative partners.
Tips
usage
Standard for institutional/business 'partner' (companies, countries, NGOs). For a romantic or life partner, use 伴侣 instead. The traditional form uses 夥 not 伙.