What is the explicit rule for the nth term of the geometric sequence?
5, 20, 80, 320, 1, 280, ...
a. aₙ=5(4ⁿ⁺¹)
b. aₙ=5(4ⁿ⁻¹)
c. aₙ=4(5ⁿ⁻¹)
d. aₙ=5(4ⁿ)