Paris stands on the Seine — option 1.

About the Seine. It rises on the plateau of Burgundy, flows about 777 km north-west across the Paris basin, and enters the English Channel at Le Havre, passing Rouen on the way. Paris grew from a settlement of the Parisii tribe on the Île de la Cité, the island in the river where Notre-Dame stands, and the city’s two halves are still called the Left Bank and the Right Bank after their position on the river. The banks of the Seine through central Paris are a UNESCO World Heritage Site, and the river carried the opening ceremony of the Paris Olympic Games of 2024, which was held on the water rather than in a stadium.

A pattern worth noting. Two of the four cities in this question stand on the Danube, Europe’s second longest river, which flows through or past ten countries and four capital cities — Vienna, Bratislava, Budapest and Belgrade. Fixing that list in memory disposes of both distractors at once.

Other well-known pairings are London on the Thames, Rome on the Tiber, Cairo on the Nile, Baghdad on the Tigris, Washington on the Potomac and Moscow on the Moskva.

Hence, the answer is Paris.