Final answer:
The correct answer is option a) Danube River, as Budapest and three other world capitals are located on its banks. The Danube is a crucial river in Europe that flows through various major cities before reaching the Black Sea.
Step-by-step explanation:
The capital city Budapest lies on the banks of the Danube River, making option a) Danube the correct answer. Four different world capitals are located along the Danube, which flows east through major European cities such as Vienna, Budapest, and Belgrade before emptying into the Black Sea. Unlike the Nile River, which is associated with the great ancient civilization of Egypt and the Amazon River, known for its massive tropical rainforest basin, the Danube has historically been central to European trade and transportation. The Mississippi River is a major waterway in North America but does not flow through Budapest or any other European capitals.