In the following code that uses recursion to find the greatest common divisor of a number, what is the base case?

```
public static int gcd(int x, int y)
{
if (x % y == 0)
return y;
else
return gcd(y, x % y);
}

```
a. gcd(int x, int y)
b. if (x % y == 0)
return y;
c. else
return gcd(y, x % y);
d. Cannot tell from this code

b. if (x % y == 0)
return y;