Duolingo has a nice interface for questions where you need to match up pairs of items. It almost certainly exists in other systems.
Two sets are displayed in columns. You click one item from one set, then another item from another set. Once you've selected an item from both columns, they're paired.
Problems:
How to show that two items have been paired? A line? Move them to the top and style them?
How to change your answer? Make paired items still selectable, or clicking on them undoes the pairing?
Duolingo has a nice interface for questions where you need to match up pairs of items. It almost certainly exists in other systems. Two sets are displayed in columns. You click one item from one set, then another item from another set. Once you've selected an item from both columns, they're paired.
Problems: