Final answer:
Runoff from farms is not an example of point source pollution; it is considered nonpoint source pollution because it comes from multiple sources over a wide area. Therefore, the correct option is C.
Step-by-step explanation:
The nonpoint source pollution refers to pollution that originates from diffuse sources and is not easily traceable to a single discharge point. This contrasts with point source pollution, which comes from specific, identifiable sources such as drainpipes, effluent pipes, and sewer outfalls. Among the choices presented -- drainpipes, ditches, runoff from farms, effluent pipes, sewer outfalls -- runoff from farms is not an example of point source pollution. Instead, it is classified as nonpoint source pollution because it is pollution that enters the environment from multiple sources over a wide area, such as pesticides, herbicides, and fertilizers from agricultural lands.