Which of the following rivers is the world's busiest waterway?

A. Rhine

B. Rhone

C. Danube

D. Seine

The river that is considered as the world’s busiest waterway is the river of Seine, letter D. it flows directly into the English Channel. It is a 350 mile long arm of the Atlantic Ocean situated between the south coast of the United Kingdom and the north coast of France.

D. The Seine. It's a 777 km long commercial waterway near Paris. Its very crowded because of the cruises that go along the river and because of its location near Paris.