Final answer:
The Danube River flows along the Hungary-Slovakia border and is a major river in Eastern Europe, contributing to the region's ecosystem, economy, and culture.
Step-by-step explanation:
The river that flows along the Hungary-Slovakia border is the Danube River. This significant European river flows from southern Germany through various countries, including Austria, Hungary, and Slovakia. It then continues its journey through the Balkans, eventually emptying into the Black Sea. It is known for its historical importance in trade and transportation, as well as for being a natural division for countries it flows through. The Danube is indeed an important geographical feature for Eastern Europe and plays a vital role in the region's ecosystem, economy, and cultural exchanges.