Re: to native speakers of english
A: The person has offered you something. When you decline an offer, you express thanks and/or regret that you cannot accept the offer.
B: Both people are rude here. Does the student order the teacher to do something where you are? They don't here. They teacher could give permission for the student to do it.
Please pay attention to capital letters. They are important.
You don't have to write "please answer me." The volunteers who come here answer people.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.