Answer:
(A) If a book was published in the past 150 years and is historically insignificant, it will probably deteriorate completely.
Explanation:
This is the overall idea of the passage. Initially, the author explains how these books deteriorate themselves and then explains how this can be avoided. Finally, he/she presents the idea that there are techniques to prevent some books from completely deteriorating, but the process of deacidification will only be implemented to books which have historical significance.
Maybe, someone else had that written? and she wanted them to have it but as i read your essay you did great on it, i see no reason to remove it ask her why do you have too..?