Which of the following expressions is equivalent to GCD(an−1,am−1)\text{GCD}(a^n - 1, a^m - 1)GCD(an−1,am−1) for a>1,n,m≥1a > 1, n, m \ge 1a>1,n,m≥1?
aGCD(n,m)−1a^{\text{GCD}(n, m)} - 1aGCD(n,m)−1
aLCM(n,m)−1a^{\text{LCM}(n, m)} - 1aLCM(n,m)−1
GCD(an,am)−1\text{GCD}(a^n, a^m) - 1GCD(an,am)−1
an+m−1a^{n+m} - 1an+m−1