I was inspired recently by @jeffatwood 's excellent article about The God Login where one would ask:
What would God do?
Well if God was doing this, there wouldn't even be a selection list - the option the user wants would be right there already - no selection necessary. God already knows which one you want.
The drop down is being used for someone to pick a bunch of questions from a drop down and add them to a list. God wouldn't need a drop down. God would just give you a list of questions and as Jeff says: Bam. One Step.
OK - but say the teacher does want a bit of control over what goes in the list, and the drop down is needed. Well they want to be able to see which ones they've added, sure (like @JonW said) - but they're more interested in the one's they haven't added yet. They can already see which one's they've added because they're right there in the list of questions they're building.
Let's imagine the worst case - 100 questions in the drop down. The teacher sequentially adds number 1,2,3,4,...99. Starts off well, but by about item 60 the teacher has to scroll way down the list to get the next one.
Well God would say you should only need to look at the list once and select everything in one go. Bam! So that means some way of keeping the list open and making multiple selections - like a multi-check list.
But what if the order mattered and it didn't match the order in the list. Well just add the questions in the order that the user clicked on them.
But what if the teacher did want to do it in more than one step. Then the list needs to allow multiple selections and show which ones have been added already.
But what if the teacher wanted to be able to see the order in which they're making a selection - while the list is still up. So maybe the list slowly fades the colour of an item in or out as the items get selected so the items age. And not only that, God would let you shuffle items around in the final list of questions too.
God still wants you not to use a drop down list so maybe God combines the functionality of the list of final questions and the above functionality of the drop down list into a single component where you can promote, demote, shuffle, and randomize one or more (or all) items at once.
What I'm saying is - you choose your priorities and think about the absolute best possible outcome - the path of least resistance - the option that seems like the system is reading your mind - the way God would do it. And see how close you can get.
Hell yeah - The God Login is the way we should be thinking!