This is a tough question.
Though, I would believe out of them all, it would be D, "animals in agriculture are deliberately bred". Animals in agriculture have one sole purpose; food. Cows produce meat and milk, pigs produce pork chops, bacon, and ham. Chickens produce eggs and meat.
Overall, they aren't used to much, and I would indeed say they're overbred. Their immune systems have never been compromised, so they have not built up a tolerance to illnesses.
Good luck!
