Apologies if this feature already exists. I am wondering whether it would be possible to allow users to go back and look at a question from a particular exercise/quiz/test they have done in the past. Sometimes I fail to understand a question (even with the worked solution), but later in the day suddenly think of something. It would be really helpful to be able to review the questions that I did in previous exercises (noting that if you redo the exercise normally, it's different questions). Thanks and thanks for Khan Academy in general; it's fantastic! :)