A committee of directors, exclusive of any active officers of the bank, must, at least once during each calendar year and within fifteen months of the last audit, make suitable audits of the trust activities or cause suitable audits to be made by auditors responsible to the board of directors, and must ascertain whether the trust activities have been administered in accordance with law and sound fiduciary principles. The board of directors may, instead of the periodic audit, adopt an adequate continuous audit system. A report of the audits and examination required under this section, together with any action taken, must be noted in the minutes of the board of directors.