I find a huge component to Main Conclusion questions is referentialphrasing, which JY talks about in the early grammar portion of the curriculum. Many times you’ll have to synthesize a conclusion from parts of multiple sentences.
I started reading Frankenstein which isn't very simply written. Lots of long sentences and referentialphrasing. I really enjoy it but also think it has the potential to get my used to the RC writing styles? Killing two birds with one stone.