1. What is a scene graph? 2. List and describe the three types of nodes that can appear in a scene graph. 3. What is FXML? 4. What is an fx:id? Why is it important that you assign an fx:id to a component in Scene Builder? 5. What is the purpose of the main application class in a JavaFX application? 6. What is the purpose of the controller class in a JavaFX application? 7. What is an event listener? 8. Describe the steps for registering a controller class to an applications GUI in Scene Builder, and then registering event listeners to specific components. 9. Why should a group of RadioButtons belong to the same toggle group?