I graded these all at once, so the grades may not be entered in the same order you made the posts. I realize this means it's not immediately clear which grade you received for which post, but hopefully you'll be able to sort that out be asking yourself a few questions about any less-than-stellar grade:
Did you say something new in the thread? Did what you wrote add to the discussion in a meaningful way?
Did you meet the requirements of the prompt - especially in terms of quotes from the book, etc.?