I think the answer is positive feedback. hope this helps! :)
Yes, students do experience more sleep deprivation than other non students because most students stay up late at night studying for pop quiz's, exams, etc. They're probably staying up doing homework, projects, make-up work, etc. They might also be stressed out which will cause most of them to be awake at night thinking about what they are stressed out about. While other non students don't have to really worry as much as these things because they aren't in school anymore.
The Sumerian plow is most like c. a tractor.
Hope this helps! :D