When the single source of pollution can be identified, it is called
a. runoff.
b. waste.
c. nonpoint-source pollution.
d. point-source pollution.

Option D point source pollution

Explanation: The pollutants which can be tracked, from the source of origin are termed as point source pollution. This can be water source, air or even light or noise pollution. The pollutants are easily detected being released from the source of pollution. Whereas the non-point source of pollution are those which are indirect sources and they carry off the pollutants which lie on the way, like runoff water carrying the pesticides from the agricultural land. Runoff and waste are examples of non-point sources of pollution. Thus, option A and C are incorrect answers.