Answer: The right answer is the <em>Moldau</em> (in German) or the <em>Vltava</em> (in Czech).
Explanation: Just to elaborate a little on the answer, it can be added that this piece is part of a larger work called <em>Má vlast, </em>which means “My Homeland,” completed by the Czech composer in 1874. <em>The Moldau</em> is the most popular of the six movements and it describes the course of the Vltava as it flows through the countryside and into Prague. Smetana composed it with a nationalistic and patriotic agenda in mind, and so it was received and embraced by his countrymen.