My Critical Reading Score fluctuates a lot, ranging from 600 to 750. I normally get bad scores when i get topics about arts, literature analysis, and history. To be particular, when I took the Official Guide practice tests, I got 630 CR on test 7, 680 CR on test 8, 750 CR on test 9 but only 600 on test 10.
I hope that you can relate my case to some students you taught in the past and help me with this. Thank you.

I think you need to figure out, more specifically than you have, what goes wrong when something goes wrong. Those topics are on every test, including BB 9. Go back through the passages that gave you trouble, and for every single wrong answer choice (not just the ones you picked, every single wrong answer choice in every question—4 per question) write down why, according to the passage, you should have been able to eliminate that choice. This is tedious, but it can also be illuminating.