What does the visible groups setting do for a quiz (in the common module settings area at the end of the editinf form)?. I understand no groups and separate groups but I don't understand visible groups. The help page at
All students submits their assignment within a single Assignment area but may choose which Group to associate their submission with before uploading. Teachers/trainers can sort submissions by Group or view All Participants.
But there seems to option for choosing your group when submitting a quiz.