Answer:
B: Genetic Diversity
Step-by-step explanation:
Humans have been breeding species of dog for centuries, which all came from one common ancestor, the wolves. These wolves were then domesticated and bred to genetically create new breeds of dogs such as the long Daschund, or the horrific demon that is the Chihuahua. Anyway, the dogs are all still dogs, not different species, meaning it can't be C, same thing applies with A. And it can't be D because they don't make up any complex ecosystem, because dogs are carnivorous mammals.