Mother:I must send out these letters today, but I don't have time. Daughter:I'll mail them for you on my way to school. Mother:_________ Daughter:Don't worry. I won't let you down.
(A)Thank you very much.
(B)It's a pity that I have to bother you.
(C)It's very nice of you to help me.
(D)You won't forget, will you?