I believe the right answer is A. The narrator is unreliable because his emotions about the cat run from attentive and loving to cruel and violent.
First of all, the narrator of this story is definitely unreliable. He tells us the story from his own viewpoint, clearly trying to somehow manipulate the facts to his advantage. He tries to explain that he suddenly started hating the cat because he succumbed to alcoholism. But it isn't persuasive enough, just like the fact that he suddenly started abusing his wife can't be explained by alcoholism alone. Still, we have the information that this abusive behavior started when they got married - which might mean that he wanted to get rid of her, and thought that the best way to do it would be to act crazy and blame the cat for all the mischief. That would help him avoid the death sentence for murder.
