I think the best answer is B. Even this is the broadest case for the Conservation of matter and the one for Energy, the only way this can be applied is in nuclear rxns.
I don't know what model you're referring to so I can't answer the question. However, upon researching, I found a similar problem. I posted it as an attached picture. Looking at the model, the amount of grams a herbivore eat each day corresponds to the arrow pointing inwards. Since the label says 4.0 g,
<em>the answer is 4 g per day</em>.
The answer is B because the mice and foxes are in competition for limited resources with eachother