Drag and drop

Hello everyone!

I am trying to create a drag and drop knowledge check that allows the drag sources to go into multiple drop targets. However, once one drag source is dropped onto a drop target, I want that drop target to not be available anymore to the rest of the drag sources. The reason why I want the drag sources to go into multiple drop targets is because the drag sources can be placed in any order. The issue I am having is that because multiple drag sources can be dropped onto multiple drop targets, the learner can drop two or three in the same drop target. The drop targets in my activity are the empty boxes below. Is there a way to do what I want to do: assign multiple drag sources to multiple drop targets but once one drag source has been dropped onto a drop target make that drop target unavailable for the rest drag sources that originally were assign to it as well? Please and thank you!