Professor Hartleys new book on moral philosophy contains numerous pas

can someone explain how option D is the correct answer.
I picked B as the answer

Pre-thinking:

Conclusion: Hartley has been dishonest in not acknowledging the intellectual debt owed to Lawrence.

Premises on which it is based:

i) Prof. Hartley’s new book on moral philosophy contains numerous passages that can be found verbatim in an earlier published work by Hartley’s colleague, Prof. Lawrence.
ii) These passages were unattributed in Hartley’s book.

The thrust of the conclusion is on the "dishonesty" in "not acknowledging" the "intellectual debt" which is purportedly owed to Prof. Lawrence by Prof. Hartley. The stimulus clearly assumes that Prof. Lawrence was the first to come up with the ideas contained in those passages (since otherwise the "intellectual debt" would not be owed to Prof. Lawrence).

Let us consider the options.

(A) Hartley could not have written the new book without the passages in question. Even if he could have written the new book without these passages, the fact that they were not attributed ensures that the conclusion remains valid. Eliminate.

(B) While writing the new book, Hartley had access to the manuscript of Lawrence s book. This is a tempting answer option, on first look. However, I am not happy with the usage of the word "manuscript", which typically means a pre-published version of a book, article etc. Even without a manuscript, Hartley could have copied the passages from Lawrence's book after it was published. Eliminate.

(C) A book on moral philosophy should contain only material representing the author’s own convictions. The reason for the "dishonesty" is not that the book contained others' ideas, but that such borrowing of ideas was not attributed to the supposed original author. The conclusion does not depend on this assumption. Eliminate.

(D) Lawrence did not get the ideas in the passages in Question or did not get their formulations originally from Hartley. Correct. If Lawrence had got the ideas from Hartley, then Hartley would not owe any "intellectual debt" to Lawrence, and thus not have been dishonest in not acknowledging it.

(E) Hartley considered the passages in question to be the best possible expressions of the ideas they contain. This is irrelevant to the conclusion. Eliminate.

Hope this helps.

Prof. H's book contains passages found in Prof L's book. So, prof. H did not acknowledge Prof.L's contribution.

While arriving at this assumption, the author is assuming that Prof. H did not help Prof.L.

Hence option D.

Some key pointers on assumption questions:
For an assumption question to be presented, there has to be a gap in the logic or jumping from topic A to topic B w/o a clear reference to topic B.

Because of this, we have two ways to approach a question:
1. Negate the answer choices.
2. If you find the gap, look for this gap in the answer choices. The answer choice which closely addresses the shift in the gap is the assumption.

Bunuel, please provide OA. I just can't eliminate B here. Thanks