When is ‘may’ most often used to ask for permission?

You're a student and you formally ask a teacher for permission to leave the room. Which sentence is appropriate for the situation?

I __________________ get good grades, so I can go to university.

I _________________ wear my ID every class. It is mandatory.

People _____________ avoid drinking alcoholic beverages because it is bad for the health.   

If I get good grades, my parents will give me a new cellphone. 

If the rider wears his helmet, he will not be given a ticket of violation by the police officer.

If the rain stopped, the class would continue.

If Cecil did not run through the heavy rains, she would not be sick. 

If the rain had stopped, the class would have continued.