Letting the User Select the Question Bank

I would probably go with the scene based branching scenario with some sort of radio buttons to use for a selection. You already have 5 question banks. Match the number of scenes with the number of choices you are planning to have on the selection slide. If your choices are A, AB, BC, AC and ABC, create 5 scenes and into each scene import the question banks that match your choices. For instance, import the question bank A into the scene A, import the question banks A i B into the scene AB and so on. Insert 5 radio buttons on your selection slides and name them accordingly. You will need the triggers on the selection slide. For example, If ABC is selected, go to Scene ABC where you just put A, B & C question banks; if AB is selected, go to Scene AB where you imported question banks A & B. Do the same for all other choices. I have attached my story example that goes more into details and the link with this example you can play with to see if this could be similar to what you are looking for. 
https://360.articulate.com/review/content/f19889bb-97a9-4203-8639-961dbc7e20a9/review