Вставьте пропущенные слова don t /doesn t или mustn t. we make noise . my little sister is asleep. i spend mush money . i do this exercise in writing. he forget to mail this letter tomorrow.

We mustn't make noise. My little sister is asleep.  
I mustn't spend much money .
I mustn't do this exercise in writing.  
He mustn't forget to mail this letter tomorrow.