Which river, known as the 'Black Dragon' in Chinese, forms roughly 1,600 kilometres of the south-eastern border before emptying into the Strait of Tartary?

• A The Ussuri
• B The Argun
• C The Zeya
• D The Amur ✓

The Amur is the world's tenth-longest river, and its basin supports a unique ecosystem including the endangered Amur tiger and Amur leopard.