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 mustnt make noise. My little sister is asleep. 
I mustnt spend much money .
Imustnt do this exercise in writing. 
Hemustntforget to mail this letter tomorrow.