The correct option is C Foxes
A food chain is a linear network of links in a food web starting from producer organisms (such as grass or trees which use radiation from the Sun to make their food) and ending at apex predator species (like grizzly bears or killer whales), detritivores (like earthworms or woodlice), or decomposer species . Here foxes are the predators of mice. Thus, if a farmer put out poison and poisoned all the mice, foxes might also be poisoned.