Which of the following is an example of nonpoint source pollution?

Nonpoint source pollution refers to contaminants that come from multiple, diffuse sources rather than a single identifiable origin. Pesticide runoff from agricultural fields is a prime example of this type of pollution because it occurs when rain or irrigation causes pesticides applied to crops to be washed off the land and into nearby water bodies. This runoff collects pollutants from various agricultural practices across large areas, which makes it difficult to pinpoint a specific source, thereby qualifying it as nonpoint source pollution.

In contrast, factory discharge and wastewater from treatment plants are examples of point source pollution because they originate from identifiable, fixed locations. Similarly, oil spills from tankers can be traced back to specific vessels and locations, categorizing them as point source pollution as well. Thus, pesticide runoff represents the diffuse and widespread nature of nonpoint source pollution, making it the correct choice.