If n is a natural number the 9^2n - 4^2n is always divisible by?

Both A & B

None of these

5 (as 9^n - 4^n is a difference of two odd powers, which is always divisible by 5)

13 (as 9^n - 4^n can be rewritten as (13-4)^n - 4^n, which is always divisible by 13)