Well, to dehumanize means to treat someone as if they weren't human. So, from this we can already eliminate A and D because they have nothing to do with being treated badly. Now, if you look at C, it doesn't necessarily talk about being treated badly, but if you look at B, it says his master was cruel, which means his master treated him and others badly.
So, I would say the answer is B.
Hope this helps!
