Choose the correct modal verbs to complete the sentences

1. Jack [can|must] chit-chat with his friends a bit because he knows the lesson topic very well.
2. Anna [must|can] wear a uniform because it's a rule.
3. I [mustn't|can't] speak French because I don't know it.
4. I [mustn't|can't] do maths exercises at all.
5. Remember that you [mustn't|can't] take selfies during a lesson.
6. Wow! My best friend [can|must] speak 3 languages!