Answer:
A. "I'm glad you had a good reason to do this."
Step-by-step explanation:
This appropriate response is the best approach to be taken by Black because he is expecting Red to admit to the fact that he carried out the fraud irrespective of his reasons.
He would lead him on to admit to the fraud by stating his reasons. Red's admission to the fraud and stating the reason he carried out the fraud (whether good or bad reason) would nail him, thereby leading to Black concluding his investigation.