Hello @KateChristie
Thanks for posting this in the canvas Community!
I totally understand how that can be a bit confusing/frustrating for students. With quizzes in Canvas, multiple drop down type questions will not cross out options that they have already selected from the list. They are only able to click the the drop-down menu and select an answer that applies to the question they are answering.
I do see how this would be helpful when you are using a bunch of dropdowns for your question(s). I think instructors typically will put in distractor answers there to really test the students knowledge. This currently doesn't exist, unfortunately.
I did see that there is some conversation about this functionality, but it is related to matching questions and multiple choice.
Would you be interested in submitting an idea for this on multiple drop down questions? HERE is a link to where you can do that.
-Colton