Final answer:
The second-longest river in Europe that starts at the confluence of the Breg and Brigach in the Black Forest is the Danube. The longest river is the Volga. The Rhine and Thames are other significant rivers in Europe, but not the second-longest. The correct answer is option a) Danube
Step-by-step explanation:
The second-longest river in Europe, which begins where the streams Breg & Brigach merge in the Black Forest, is the Danube. The Volga River is actually the longest river in Europe, stretching through Russia and playing a crucial role in transportation and as a source of fresh water.
The Danube is known for flowing through various major European cities, such as Vienna, Budapest, and Belgrade, eventually emptying into the Black Sea. In contrast, the Rhine River originates in a similar region but flows north and empties into the North Sea in Rotterdam, which is notable for one of the world's busiest ports.
Additionally, the Thames is a much shorter river located in England, known primarily for flowing through London.