Unable to unselect some options in pick many quiz

DevinOToole​ : The problem is that you only have 1 option listed as a choice in Form View: 

That 1 option is the only one recognized as a possible answer to the question. If it's not Selected when the user clicks Submit, the program will show the "Invalid Answer" warning.

The other buttons will toggle between their Selected and Normal states as the user clicks them. But the selection of one doesn't impact the other buttons.

The solution: In Form View, you need to indicate every object that is a possible response. 

When you do that, Storyline automatically puts those objects into a Button Set, so only one can be Selected at a time. 

For more information:

•  Storyline 360: Converting an Existing Slide to a Freeform Interaction | Articulate - Community 
•  Storyline 360: Working with Button Sets | Articulate - Community 
• PRIMER: Take advantage of built-in states | Articulate - Community