Can you disable or mask buttons after a question is answered?

I am a newbie and trying out functionality in Storyline.

I have a simple question with two clickable buttons. That works fine. However, I set up a final trigger so after Button A or B is clicked, a Mask layer displays. It covers the buttons with a transparent shape so learner can't try the other answers. That doesn't seem to to want to work; the answers to the question don't show up, but the Mask does.

Is there a way to do both?

Thanks,

Ken V.