Answer: c. pesticide runoff
Explanation: A point source pollution is the pollution which is caused by the pollutants whose source of origin can be traced back and further pollution can be prevented. A non-point source pollution is the one which cannot be traced back to it's origin and hence, cannot be prevented from further pollution. Trash dumping, sludge dumping and oil spill are the examples of point source pollution. But pesticide runoff is the example of non-point source pollution. A surface runoff will wiped off the pesticides from their surface and discharge them to the water body the source of origin of these pesticides will remain undetermined.