Which of the Following Is the BEST Negative Reply to a Request

Multiple Choice

Which of the following is the BEST negative reply to a request for a favor?

A) Thank you for asking me to speak at your meeting, but I will not be able to attend.
B) Because I have a previous engagement in Phoenix, I cannot demonstrate my machine at your conference.
C) Although I have multiple obligations for the date you suggested, I fully support your effort to raise funds for the homeless.
D) I find my schedule is as impossible as ever; I must be doing something wrong with my priorities.