Answer:
I'm leaning towards A here.
Explanation:
Let's skip A for now. For B, it states that the squrrel...now think about it. Squirrels don't connect with deers so it probably isn't that. Next is C. It states that the grass population would decrease, however it may actually increase because then only the mouse is eating in (in this graph of course) and so D cannot be correct either. Now with A, it states that the coyote population would decrease. Now I don't know if this is very likely however it does make sense and so I think it's that.