Dear Professor [Name],

I am writing to request an extension on the [Assignment Name] due on [Date]. Due to [reason for extension], I am unable to submit the assignment by the due date. I understand the importance of submitting my assignments on time and would like to assure you that I have been working hard to complete it.

I would be grateful if you could give me an extension of [number of days] days to submit the assignment. I understand that any extension is solely at your discretion and I will adhere to any deadlines you set.

Thank you for considering my request.

Sincerely,
[Your Name]
Scrivi una lettera di richiesta a un professore chiedendo una proroga nella presentazione di un incarico.