In the book, the author says that kids can change the world by changing their eating habits
I think this is saying that Josh's dad wants to teach Josh what it means to do something really well.
What I know of Sister Mary Joseph is from a disease. It is a nodule. Anyway, according to context, the best answer would be letter C. The word that best describes Sister Mary Joseph is Spiritual. This is because of the amount of biblical reference from the names.