Wrong trigger. (A) would allow us to conclude that we cannot fully understood the e-book if we don’t understand the media that came before it. But we don’t know that we haven’t been able to understand the media that came before e-books (printed books). So (A) doesn’t strengthen this argument.

This principle allows us to conclude that an electronic medium is more similar to other electronic media than it is to print media. But we’re trying to conclude that we can’t understand the e-book yet. The similarity of e-books to other electronic media doesn’t reveal anything about our level of understanding e-books.

(C) doesn’t help us reach a conclusion about lack of understanding. We know that e-books haven’t taken their ultimate form. (C) tells us the ultimate form depends on technology. But what does failing to achieve the ultimate form imply about our understanding of e-books? We dont know.

(D), restated, tells us that if we haven’t observed the evolution of a medium’s content, then we cannot understand the medium. We know from the premises that we haven’t observed the evolution of e-book content. Right now, it still carries the content of print books; we haven’t seen the ultimate form of content that will be contained in an e-book. (D), then, allows us to conclude that we cannot understand e-books.

(E) concerns what’s required in order for one medium to replace another. But it doesn’t tell us anything about what’s required in order to understand a medium. We’re not trying to prove that e-books can’t replace printed books. We’re trying to prove that we can’t understand e-books yet.