A、  B、  C、  C所给出的问题是一个以Why don’t I…，“不如我(这样做)……怎么样?”开头的疑问句。这类疑问句一般用来表示建议。因此，选项(C)表示对对方提议的肯定回答，是符合语境的正确答案。另外应记住Why

Do you have the receipt for the office supplies?
(A)Yes, I’m sorry. I forgot to give it to you.
(B)We have one ink cartridge for the printer left.
(C)No, I usually buy office supplies from Office Giant, downtown.

Why don’t I give you my accountant’s number?
(A)I’ve used him for three years.
(B)No, I don’t have an accountant.
(C)That would be very helpful.