Hello,
While I was preparing for SAT, I found this sentence:
“Quick to take advantage of Melanie Johnson’s preoccupation in the history of the Johnson family, the genealogist proposed investigating that history-for a large free”
it is said that “preoccupation in” is the wrong part of the sentence, but I didn’t know why, so please explain this to me
I believe it should be “preoccupation WITH” instead of “IN.” When you’re busy you are occupied with tasks that you have to do, not occupied in them. I know that’s not the most thorough explanation but I hope that helps 
Yes, this is an idiom error. Preoccupation should used with “with”.
Thank you both for your help.