An investment professional has narrowed the investment choices to recommend to a client down to two mutual funds. Each choice has a ten$-$year average return of $9\mathrm{.}5\%.$ Fund A has a standard deviation of $18\%.$ Fund $B$ has a standard deviation of $16\%.$ Fund A has a relationship with the professional's registered investment adviser firm that would pay this professional a bit more than they would receive from Fund $B.$ Which fiduciary duty is the investment adviser representative dealing with in this situation?

A$)$ Duty to disclose

B$)$ Duty to diagnose

C$)$ Duty of loyalty

D$)$ Duty to consult