Rob and carla observed two trails of dogs' footprints in the mud. the spacing between the footprints in one set was markedly larger than in the other. rob concluded that one of the dogs must have been bigger than the other. however, carla had a different explanation.

which is the best alternative to rob's conclusion?
a) the two dogs were of different ages.
b) one of the dogs was in search of food.
c) the two dogs were of different species.
d) one of the dogs ran faster than the other.