Answer:
B. a fox
Step-by-step explanation:
A secondary consumer is those that, to produce energy, consume primary consumers. Those are always herbivores or organisms that only eat autotrophic plants.
In this case, a rabbit and a cow are primary consumers.
The mouse is herbivores too.
The only option left is Fox.
Foxes eat other animals, they are carnivorous. This made the fox a secondary consumer.