Human activities can alter an ecosystem and bring about the extinction of a species. such activities include any of these except a) hunting a species to extinction. b) assuring a habitat remains unharmed. c) introducing toxic compounds into food webs. d) introducing a new species into an environment.

The correct answer is option B, assuring a habitat remains unharmed

Explanation:

Among all the given options , human activities preserving the ecosystem is depicted in option B where human is not trying to disturb the ecosystem. While in all other options, hunting a species upto extinction will create disappearance of an species from ecosystem, introducing toxic compound to a food web will lead to transfer of toxic compound to each trophic level  and in the last option D,  even if a new species is introduced in the food web, it will destablize the food web thereby making the ecosystem as unstable.