Ricardo observed two trails of dogs' footprints in the mud. The spacing between the footprints in one set was much larger than in the other. Ricardo reasoned that one of the dogs must have been bigger than the other. What is another explanation for Ricardo's finding? A) One of the dogs was a mountain dog. B) One of the dogs was searching for food. C) One of the dogs was older than the other. D) One of the dogs ran faster than the other.