I think you are asking a really tough question to answer here! That said, I'm going to try my best ;p This is tough to explain because (E) is just written pretty darn cryptically if you ask me.
I see your confusion, in the sense that both (A) and (E) point to something having to do with an objection to clairvoyance (as in the original argument) relating to knowledge and process. But, since these rather abstract terms are being used in a specific way, let's try to pay attention to this. In particular, the argument sets up a definition of knowledge and then uses a hypothetical about clairvoyance to say that this definition of knowledge has been objected to. The author says essentially that this example is not a problem for our definition of knowledge because it is clairvoyance we reject, not some form of knowledge.
(A) gets at this nicely by keeping in mind precisely what is at issue - that is that there is some underlying belief about clairvoyance the author is citing to make his point - and that this has nothing to do with the definition of knowledge.
(E) is hard to get rid of, but I'd be very suspicious of the wording "the case of clairvoyance is not a case of knowledge." Not to be overly picky/lawyerly, but what exactly is a "case of knowledge?" The argument hasn't told us, and I'm not inclined to fill in a somewhat random or assumption-filled guess. To my mind, this is more than enough to get rid of (E).
Does that make sense? Please let me know if you have follow-up questions or comments on this one. I'd love to hear more from you and chat about this