Meilleure réponse !
1) You must not do your homework before dinner? or You must do your homework after dinner?   2) He may not find a cheaper car 3) You need to do the washing-up 4) You should use my computer, ("you must use my computer" sounds strange, it could be right though..depends on the context) 5) They did not have to cut the grass 6) We have to do the shopping today 7) I do not have to take my car to the garage 8) We were allowed to go swimming