Drag-and-drop: complex issue with multiple correct drop zones

Hi everybody,

I'm facing an issue that, despite my many tries, I just can't figure out.

I have this drag and drop system, with 5 answers and 5 dropping zones. Quite simple for now.
The thing is: among the 5 answers, 2 of them are identical (answer 1 and answer 5), as well as 2 others (answer 2 and answer 4). So I actually only have 3 different answers. If you ask yourself why do I have the same answers twice, it's because these answers will have to be placed on top of an image, which shows the same objects twice.

So here's what I wanted to achieve:

• Answer 1 and Answer 5 can both go on Zone 1 or Zone 5. So if I drop Answer 1 on Zone 1, and Answer 5 on Zone 5, it's correct. But if I drop Answer 1 on Zone 5 and Answer 5 on Zone 1, it's also correct.
  So 2 correct dropping zones for each of these answers.
• Answer 2 and Answer 4 can both go on Zone 2 or Zone 4 (same principle as described above).
  So 2 correct dropping zones for each of these answers as well.
• Only Answer 3 has one single correct dropping zone (Zone 3).
• Finally, there's a 6th possible answer, but that's a wrong one, it shouldn't be placed anywhere. But this answer isn't important in my problem.

Thanks to the community, I made it work with many triggers (file is attached).
However, for it to be perfectly working, I couldn't use the "classic" Storyline form where I set a correct answer for each dropping zone, simply because, as far as I know, I can only set ONE correct answer per zone (not 2).
So, except for Zone 3, I made it work with triggers.

My problem is the following: even though I've checked the "Allow only one element per dropping zone" box, this feature only works for Zone 3 (because that's the only one I could fill in the classic Storyline form, I guess).
Indeed, if I drop an answer on Zone 3, and then try to drop another answer on this Zone, the previous answer will go back to its original place, which is good.
But that's not working for the other Zones. If I take Answer 2 (for example) and I place it on Zone 5, and then I place Answer 4 on Zone 5... Answer 4 will just go on top of Answer 2, which will stay in place instead of going back to its original place... which is obviously not user friendly at all.

Can you guys think of anything to make things work?
I would really like it if only Answer was allowed per Zone ; so, no matter which Zone, if I drop an answer while there's already an answer on this Zone, the already-here-answer will go back to its original position.

Thanks a lot for you help.