Which of the following is correct? * A. The nullity of the principal obligation carries with it that of the penalty clause. B. The creditor is entitled only to the penalty and cannot demand for additional damages although there is refusal to pay on the part of the debtor or fraud in the performance of the obligation. C. Proof of actual damages suffered by the creditor is necessary in order that the penalty may be demanded D. The penalty may not be equitably reduced by the courts.