Answer:
D)Napoleon and the other pigs walking upright and acting like humans
Step-by-step explanation:
In animal farm the animals rebel against the humans that have been exploiting them, and as a result of that they came up with 7 commandments to make a living better for all animals, the first one being
"Whatever goes up on two legs is an enemy", because the only species they know that walks on two legs are humans.
The pigs are put in charge of supervising the farm life, they eventually become the exploiter and start doing the same things that humans did to the farm animals, that´s why they eventually walk on two legs, to exemplify that most of the time, when someone unfit gets to power it corrupts him.