After a copper smelter begins operation, local downwind populations of plants begin to adapt to the resulting air pollution. Scientists document, for example, that the acid tolerance of several plant species has increased significantly in the polluted area. This is an example of ...

artificial selection

over production

selective breeding

natural selection

natural selection (directional selection).

Explanation:

Natural selection: In biology, the term "natural selection" is described as one of the central concepts associated with evolution. Through the process of natural selection, different organisms having favorable traits are most likely to reproduce. However, these organisms then pass the given traits to their next or coming generation. The process of natural selection allows different organisms to adapt to their specific environment.

Directional selection is considered as one of the different modes of natural selection.

In the question above, the given statement represents a natural selection.