Which of these is most likely to contribute to the long-term instability of a local ecosystem?

It’s where a key species is still alive and where each species has a role to play and a food chain where it can kill off but still maintain the other species. Like a cat taking care of mice or a rabbit to a Fox, anything that can repopulated really quickly needs to have a predator to regulate that area. I hope that makes sense in choosing the correct answer

Idont really understand