Answer: C. competition
Step-by-step explanation:
Competition can be define as the ecological relationship in which one species is more superior over the other in deriving resources. In competition usually one species live and the population of other species may either decrease in abundance, or may extinct.
The release of toxic chemicals by the plants to harm nearby plants is an example of competition. This is because of the fact that the plants may face competition with other plants for resources such as sunlight, water and minerals. Therefore, a physiological response will be generated inside the plants so as to kill the neighboring plants.