Réponse :
a) so we musn't speak loudly.
b) We must wait until our break.
c) we must always be on time.
d) We musn't copy our friend's homework. We must do it on our own.
e) We mustn't exit the class without our teacher's permission.
Explications :
Rappel :
Must exprime l'obligation contrairement à musn't ou most not qui expriment l'interdiction