In the formula /=P-r-t, what does r stand for?
 a. Rate: the percent that interest is paid annually as a decimal
 b. Ratio: the size of the interest interval compared to time
 c. Return: how much money you end up earning
 d. Reserves: how much money you have in the investment
 Please select the best answer from the choices provided
 OA
 OB
 OC
 OD