Return the greatest common divisor of the integers a and $b.$ If either $a$ or $b$ is nonzero, then the value of $gcd(a,b)$ is the largest positive integer that divides both a and $b.gcd(0,0)$ returns $0.$ You want to write a program that makes use of this function, the last three lines of the program are shown below. What should the first line be$?$ Select the correct answer below.