How does the city basel, switzerland use the body of water the rhine river as a source

As the Rhine enters Germany it becomes the border between Germany and France. Through the Rhine Gourge the landscape changes again as the river narrows to form a steep sided-valley filled with vineyards and castles overlooking the river. Finally the Rhine reaches the Netherlands , a completely flat country, where it joins several other rivers on its final journey to Rotterdam and the sea.

Many years ago, the Rhine was considered as one of the most polluted rivers in Europe. In 1986 the river was severely polluted by a chemical factory fire (Chemical spill turns Rhine Red - BBC News 1986 ). Within 10 days the pollution had travelled the length of the Rhine and into the North Sea.

After the Chemical spill in 1986 the Rhine Action Programme (RAP) was developed, and adopted by all the countries bordering the Rhine. By the year 2000, the programme aims to achieve a return to the river species such as the salmon which once thrived there. The use of the river for extracting drinking water is also safeguarded.

i think the answer is b.