Show a warning pop-up if a user clicks the Submit button without drag and dropping all the images to a zone

Thanks for your answers :)

Here's a simplified .story file.

You'll see that the drag and drop feature works great, but I can't figure out how to show the "Unvalid answer" layer when the user clicks the Sumbit button without having drag and dropped all the 3 answers and the dropping zones (correct or incorrect).

Thanks a lot in advance_