14. Here is a simple dialogue using the expression "May I":

Person 1: Hey, can I borrow your pencil?

Person 2: May I know why you need it?

Person 1: I forgot mine at home and I need it for the test.

Person 2: Sure, here you go. May I ask you to return it to me after the test?

Person 1: Of course, no problem. Thanks for letting me borrow it.

Person 2: You're welcome. Let me know if you need any help with the test.

Person 1: Thanks, I will. May I sit next to you during the test?

Person 2: Sure, go ahead. Good luck!

15. You can say "Please take a seat" or "Have a seat" or "Sit down, please" or "Can you please sit down?", These are all polite ways to ask someone to sit down.