single switching point

Hi, is there a way to force a single switching point in questions as the one reported below? Basically, I want people once the switch from option A to option B, to remain on option B for the consequent questions as well automatically.
This is a task that people in an experiment have to play. They can choose whatever they want. The only think I would like to have is that whenever they switch from A to B (it can be after the first radio button, or after the second, the third and so on), then they can only choose B thereafter. This is basically a consistency requirement.
For example, if someone chooses A in the first three radio buttons and then switches to B at the fourth one, I would like to have that from the fourth one on she/he can only choose B, or even better than B is compiled automatically thereafter. I would like this process to work not only for the example described but in general.