Question Writer Manual/Quiz Options/Quiz Details/Pre-Randomized
Number of Pre-Randomized Quizzes 
If you're using any randomization in your quiz or sections, Question Writer handles this by generating a number of pre-randomized quizzes when you publish. One of these is selected at random each time a quiz-taker accesses the quiz. It is usually better to have more rather than less of these pre-randomized quizzes as this minimizes the possibility that two quiz-takers will see the same quiz or the same quiz-taker will see the same quiz twice in a row.
Balance this against the time it takes to publish your pre-randomized quizzes and the space that the pre-randomized quizzes will take up.
See Frequently Asked Questions for an idea of how this can be used.