Author is unaware of these facts (those that were available to anyone when the book was written) when he wrote the book
→
Accountable for misleading readers
The principle that is being purported here is that, if a person is unaware of the facts - regardless of whether or not the facts were available - that person is not accountable.
(A) This is discussing whether or not the biographer should be blamed for whether the book is favorable or unfavorable to the readers. This is not the same thing as whether or not the biographer should be blamed for misleading the readers. Eliminate.
(B) This has some conditional language ("only" when) attached to it so we can put this into a conditional format:
Facts are not omitted deliberately in order to mislead --> Author should not be blamed for readers' misperceptions
This would be a better answer if it were not for the "in order to mislead." The author never tried to mislead the readers as he was not aware of the facts when he wrote the book. In addition, this is claiming that the author should not be blamed when the argument is saying that he should.
(C) We do not know if those facts supported or didn't support the author's view. Because we don't know this, this cannot be the correct answer. All that we know is that the facts were "incriminating," but this is not the same as "supporting" or "unsupporting" of the author's view. For all we know, the author could be thinking that the politician is the most perfect human being in the world and these incriminating facts would not support the view.
(D) This says (blamed→facts are omitted). This has a lot of great language but it just simply not what we need. We need (facts are omitted → blamed). This is not it, this is a mistaken reversal.
(E) This is exactly what we need! It is saying that the author should be blamed for omitting these facts because they were widely available!