A species of plants that adapts to become more tolerant of toxic heavy metals produced as a result of human mining activities is an example of _______.

Directional selection occurs when environmental conditions favor one end of a range of traits, causing the population to shift in that direction over time. Here, mining produces toxic heavy metals, and plants that tolerate higher metal levels are more likely to survive and reproduce. So this is directional selection, choice C.

AI-written and checked against the verified answer.