Which of the following is not a prohibited mutual fund sales practice??

Question $6$ options:

a$.$ Providing frequent, non$-$monetary benefits to distributors or salespersons

b$.$ Subsidizing co$-$operative funds for general marketing expenses.

c$.$ Changing the rate of commission on a fund when renewing the prospectus.

d$.$ Providing money or goods to distributors or salespersons as client appreciation