Smetana composed a musical work depicting bohemia's main river as it flows through the countryside. the name of the river, and the musical composition, is the

The right answer is the Moldau (in German) or the Vltava (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 Má vlast, which means “My Homeland,” completed by the Czech composer in 1874. The Moldau 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.