How do I keep the questions attached to a stimulus in an item bank? 

I have created several stimulus questions, each with 3 different attached questions. When I created them, I added them to an item bank.  I would like to have a quiz pull one stimulus and its attached questions at random.  Unfortunately, when I tried to pull a random question from the item bank, it just pulled one of the associated questions without the stimulus.  If this is the case, what is the point of putting the questions in the item bank?