what is the source of this question

this question is from an online test from princeton review

i think the answer choice is saying sales revenue for genre books and sales revenue for fiction books other than genre or classic literature.

but i am still a bit confused as to why this is the answer.
the online explanation said: increasing sales of genre books would not mean these books will dominate the market if total sales of fiction books in general are increasing.
however, what if sales of genre books account for a significant part of the total sales of fiction books?

oki
the conclusion is :Critics fear that if current trends continue, genre books will dominate the market for fiction books

now if the market of the fiction book itself is expanding then the conclusion will not hold true .

lj88 wrote:Literary critics are concerned by a recent trend in book publishing. The sales of genre books—-lowbrow fare, such as romance novels, that critics contend have little literary value—-have increased dramatically over the last five years. In fact, an analysis of the books stocked in bookstores shows that the ratio of titles in the classic literature category-—which includes books with high literary value by such authors as Dickens, Dostoyevsky, and Faulkner-—to titles in the genre category has decreased over the same period. In addition, average sales per title in the genre category have increased greatly over the last five years. Critics fear that if current trends continue, genre books will dominate the market for fiction books, signaling a lamentable decrease in the quality of literature to which the average reader is exposed.

Which of the following pieces of information would be most useful in evaluating the validity of the critics claim about genre books potential domination of the market for fiction books?

A) the likelihood that current trends in the sales of books in the genre and classic literature categories continue

B) the amounts of sales, in dollars, for books in the genre and classic literature categories over the last five years

C) a comparison of sales revenues for nonfiction books and genre books over the last five years

D) sales revenues over the last five years both for genre books and for fiction books other than those in the genre or classic literature categories

E) a numerical estimate of the literary value contained in each of several representative titles of the genre book category

Quick Analysis -
Conclusion - genre books potential (will) domination of the market for fiction books
Premise -
P1. The sales of genre books have increased dramatically over the last five years.
P2. In book stores - ratio of titles in the classic literature category —to titles in the genre category has decreased in last five years
P3. average sales per title in the genre category have increased greatly over the last five years

All three premise hints at, though don't directly state, that there is decline in sales of classics.(smart..i almost fell for it). P2 and P3 doesn't even tell us anything about sale trends of classic to genre. P1 just says that there is increase in sales of genre books, but that doesn't mean that sale of classic has stayed same or decreased

I would look for an information that proves that there increase in volume of fiction as a whole (i.e. the size of pie has increased)

Now lets look at the answer options.

A) the likelihood that current trends in the sales of books in the genre and classic literature categories continue - Doesn't help at all. As no trend is clearly told by the argument

B) the amounts of sales, in dollars, for books in the genre and classic literature categories over the last five years (Through this would help, but volume in number would be better then dollar value)

C) a comparison of sales revenues for nonfiction books and genre books over the last five years (Non-fiction : genre would not be a helpful indicator. Non-fiction is beyond the scope)

D) sales revenues over the last five years both for genre books and for fiction books other than those in the genre or classic literature categories (now a new element has been added - fiction other then classic and genre. So now fiction pie has three elements - Classic, genere and others. If i know value of Genre and Other, can i comment upon share and size of pie. May be/May not be- Inconclusive)

E) a numerical estimate of the literary value contained in each of several representative titles of the genre book category (comparison of literary value contained in each of the book is beyond the scope)

I would still go for B and not D.

Please let me know if I am missing out on anything in D