A vs E

Good question, this is a tough distinction but I think we could sum it up by saying that the author can agree with a statement, and even incorporate it into their argument, but it wouldn't be a necessary premise. That is, without that premise the argument would still stand based on the other premises. I'll try an example. We could say "dogs are better than cats. The purpose of a pet is to provide companionship and dogs are clearly better at this. In addition, dogs are less likely to be jerks than cats." In this case, the argument would stand without that final sentence. The author is using it and agreeing with it, but the core of the argument is the first two sentences and the final one is not necessary to the argument. I think that E fills a similar role.

Ah I see, thank you Emil. So this is a Necessary Premise question?

I think it is! Pretty rare for rc but this is one of the few