b. Unexploded WWII bombs have been exposed is not a result of the low water level of the Danube River.
Step-by-step explanation:
Unexploded WWII bombs were found in river Rhine in Cologne. As the river reaches its extreme low level the unexploded bomb from Second World War was exposed. The weight of the bomb was between 50-125 kg.
Danube River was second longest river in Europe. Danube River flows through almost ten countries. Drying out of river may cause dying of fish in large numbers.
The ships and barges are left stranded as the water level in the river reduces extremely.