The answer is:
Greg pushed the button over the bell marked Ridley, thought of the lecture he knew his father would give him, and smiled.
A dynamic character experiences an important, internal change through the events of a story. In the sentence from "The Treasure of Lemon Brown", by Walter Dean Myers, Greg Greg is a dynamic character because in the beginning of the story he is upset and doesn't want to hear sermons from his father. However, at the end of the story he understands his father wants the best for him and is happy to have him.