You must/mustn't sit on a table.
mustn't
You must/mustn't play in the traffic.
mustn't
You must/mustn't wear a helmet.
must
You must/mustn't play with the electricity.
mustn't
You must/mustn't listen to the teacher.
must
You must/mustn't run in the class.
mustn't
You must/mustn't play with the plug.
mustn't