needn't,must ,mustn't
Teachers needn' t wear suits for work, but their clothes must be neat and clean.
Students.mustn'tuse their mobile phones during the lessons.
You needn't arrive on time for lessons. It's important not to be late.
You needn't eat lunch in the school canteen. Some students prefer to go home for lunch.
students and teachers must  be polite to each other.
You must buy a coursebook, your teacher will give you one.
You mustn't eat or drink in any of the classrooms.
Students must take an exam at the end of the year. This shows how much they have learnt.

Students in VietNam must wear uniforms when they are at school

xin lỗi vì chỉ làm 1 bài nếu giúp được cho bạn thì nhớ đánh gái 5 sao nha

1. Teachers needn't wear suits for work, but their clothes must be neat and clean.
2. Students mustn't use their mobile phones during the lessons.
3. You must arrive on time for lessons. It's important not to be late.
4. You needn't eat lunch in the school canteen. Some students prefer to go home for lunch.
5. Students and teachers must be polite to each other.
6. You needn't buy a course book, your teacher will give you one.
7. You mustn't eat or drink in any of the classrooms.
8. Students must take an exam at the end of the year.