Need help with Robotics in ROS questions. Please give clear and correct solutions. Thank you.

3 Questions 1. What is a ROS Service? If you were to generate 2 additional useful services for turtlesim what would you add? 2. What is a teleop node and what messages does it output? Explain in basic form how you would use this. 3. Create a graph outputting the difference in distance between the two turtles in turtlesim. Put the graph in your report and talk about it? ex. Does it make sense? Are there any irregularities? What is a way you can improve how the turtles follow eachother? 4. Using what you have learned, explain in your own words how you make a robot follow another robot/human/object