Choice-A is the one that describes compound interest.
A is the value of the account after some time.
P is the principle. the amount you originally put in, before any interest.
r is the interest rate
n is the number of times per year that interest is paid
t is the number of interest payments that have happened
since you first put the money in the bank.
The answer should be A as it best satisfies the equation of compound interest
; where A is the value of account, P is principle, r is rate, n is frequency of interest payments per year and t is time.