Kylie starts with $145 in her piggy bank. Each month she adds $20.

Which recursive function rule models the total amount in Kylie’s piggy bank at the end of each month?
A. an=20⋅an−1​ and a1=145
B. an=20+an−1​ and a1=145
C. an=145⋅an−1 and a1=20
D. an=145+an−1 and a1=20