Which of the following openings is most appropriate for a direct claim letter?

A、For the past four years, we have held our annual banquet at your fine restaurant.;
B、On January 31 a number of our employees attended a banquet at your restaurant.;
C、Please process a refund for $68 to reimburse us the amount we were overcharged for our banquet.;
D、We were extremely upset to learn that we were charged too much for our banquet.