Dear David,
Thanks for your answer.
Good! Tomorrow I will tra with your solution.
My goal is:
A student must to see 1hour video lesson.
In this 1hour must appears random and suddenly 4 quiz moments. Then if a student give the wrong answer, he must to return at the beginning of that part and retake the quiz in a different moment.
And so, for example, if at the first attempt, the quiz was appeared at 14:30 min, at the secondo attempt the quiz must to appears at 13:15 min...and so on...
I hope your solution solve my problem