Fill must or must ' t

Sure! Here are some sentences filled with "must" or "mustn't":

1. You **must** wear a helmet when riding a bike.
2. You **mustn't** talk during the movie.
3. She **must** study hard to pass the exam.
4. You **mustn't** leave the door unlocked at night.
5. We **must** finish our project by Friday.

If you have specific sentences you'd like me to fill in, please provide them!