Monique Has Decided That She Must Apologize to a Customer

Monique has decided that she must apologize to a customer in her buffer.Which of the following is the best example of an effective apology?

A) We apologize for any inconvenience this has caused.
B) You have every right to be concerned, and we sincerely apologize for the delay in filling your order. To prevent this from occurring again, we have upgraded our software and retrained our order takers.
C) We regret that you were not happy with the situation.
D) We are sorry and admit that we are completely responsible and take full legal responsibility for this situation.