The sum of terms of a series is $\frac{2^n-1}{3}$.What is the type of series AP or GP. What is the value of d or r (common difference of AP or common ratio of GP)

Question

$(a)\;AP,d=2\qquad(b)\;GP,r=2\qquad(c)\;AP,d=5\qquad(d)\;GP,r=3$