Triggers and Variables

Hello Heroes,

This is a trigger/variable question that I have. Here is my scenario:

I have a menu type of screen made up of doors. When the user clicks a door it takes them to a scene. When they complete the scene it takes them back to the doors, where they choose the next topic.

Each door has 3 states: open, closed and closing. If they haven't completed the topic it's open. If they have it's closed. The third state, "closing" is where I need help. I need this state to show the door closing only when the user has JUST completed the topic. How do I tell the slide with the doors on it which topic the user completed LAST, and thus, which door to show closing? Each door will only be shown closing once. If they revisit the topic I need it to remain closed.

Thank you!