Click Reveal

I did not see a trigger to change the state of the Next button to normal.  I added a trigger to your 4th button (Environment). It changes the state of the Next button to normal when the state Environment is Visited. Since you are forcing the learner to select the buttons in a specific order, and the Environment button is the final one, the next button can change to normal when the button is visited.  

I believe it is easier to separate the button from the text when creating an interaction like this.  It is easier to manage.  The attached file shows the changes to make it work.