Which Sentence Would Be the Best Buffer for a Bad-News

Multiple Choice

Which sentence would be the best buffer for a bad-news letter declining an invitation to speak at an annual Chamber of Commerce awards banquet?

A) Thank you so much for inviting me to speak at your annual awards dinner.
B) I am honoured by your invitation to speak at your annual Chamber of Commerce awards dinner.
C) I'm afraid I won't be able to accept your invitation to speak at your annual awards dinner.
D) Your annual awards dinner honouring outstanding members of the Chamber of Commerce is a prominent event that benefits our community in significant ways.