You mustn't talk in the class.

-You mustn't talk in the class.

I must not get out of the class without permission

-I must not get out of the class without permission

I must help the companions

-I must help the companions 

we mustn't use the cell phone in class

-we mustn't use the cell phone in class

I mustn't fight in the school

-I mustn't fight in the school

not paint in restrooms

-not paint in restrooms

i must use the uniform

-i must use the uniform