Dear Professor, 

I wanted to express my disagreement with your last answer to my question. I believe that the answer you provided is incomplete and does not fully consider my question. I believe my understanding of the given material is correct and that my opinion is valid. I would appreciate if you could take the time to explain your response and provide further clarification. 

Thank you for your time and consideration.

Sincerely,
[Your Name]
Oggetto: Disaccordo con la risposta del professore Gentile Professore, volevo esprimere il mio disaccordo con la sua ultima risposta alla mia domanda.
Componi un'e-mail al tuo professore esprimendo disaccordo con la sua risposta e spiega perché ritieni che la tua opinione sia valida.