Identify the rule (or formula) that generates the nth term of a geometric sequence from the choices below. a(n) is the nth term of the geometric sequence, a represents the first term, r is the common ratio, and n is the term number.

a) a(n)=a⋅r(n−1)

b) a(n)=a−r(n−1)

c) a(n)=a+r(n−1)

d) a(n)=a⋅r(a−1)