Making promises: I promise that I will finish the job on time.
I promise you that that's the truth.
I swear I will never leave you.
I swear I won't let you down.
I assure you that I will return the book tomorrow morning.
I assure you that I will be there on time.
Believe me, I won't make you disappointed.
Trust me, I can do it.
Useful Responses:
Thank you.
I believe you.
All right. Keep your promise.
I hope you will keep your words.
Just let the time answer it.
