Answer:
The correct answer is C. Europe's most important commercial river is the Rhine.
Step-by-step explanation:
The Rhine is the largest river in Western Europe. It flows into the Alps and flows from Lake Constance in Switzerland to the north and northwest through (and on the border with) Germany, France and the Netherlands to its outlet in the North Sea. The outlet is divided into several large river arms.
The Rhine has had and still has tremendous significance for trade in the countries concerned. Between the city of Basel and its estuary, the Rhine crosses one of the most densely populated areas of western Europe, historically rich in trade, and flows into the city of Rotterdam, Netherlands, the most important European port center.