Your dog has been scratching itself for the past few days. You notice that this scratching is occurring more than usual. When you take him to the veterinarian, the doctor explains that your dog has been infested with fleas. The fleas have been making your dog scratch like crazy, while making a nice little home for themselves within your dog's fur. In this scenario, what type of relationship does the dog and the fleas have?

a. mutualism
b. commensalism
c. parasitism