input: Write a python function to determine the prerequisites for a given list of courses.
  assert prerequisitesCourses([("Math", "none"), ("Science", "Math"), ("English", "none")]) == ["Math"]
  assert prerequisitesCourses([("History", "English"), ("Philosophy", "History"), ("Art", "none")]) == ["English", "History"]
  assert prerequisitesCourses([("Biology", "Chemistry"), ("Chemistry", "none"), ("Physics", "Math")]) == ["Chemistry", "Math"]
output: def prerequisitesCourses(courses):
      prerequisites = set()
      for course, prereq in courses:
          if prereq != "none":
              prerequisites.add(prereq)
      return sorted(prerequisites)