Or a sub-category. Take a look at my graphic. What I do is to randomly pick 15 questions from only Ch01 when we are into Ch01. I create a quiz based only on Ch01.
Then, at mid-term, I give the students 50 random questions from all of the first half chapters. By organizing the questions as I have, it is very easy to accomplish setting up the individual chapter, and the mid-term. I do not need to separately set up the mid-term questions. Hope this makes sense to you.
By the way, in the picture, the next upper level for me is "Business Courses".
