The class Demo Tool page is a teaching tool that allows you to run fixed instances of questions: this means that the question data will not be randomized. Each time you run the question, it will populate with the same data.

The Select Instance box allows you to enter a number which controls the randomization of the question. Entering the same number and running the question again at a later time will let you start the same instance of the question again.  Leave this box blank to start a random instance like other assignments do.