Fill in the code to complete the following method for computing a Fibonacci number.

```
public static long fib(long index) {
if (index == 0) // Base case
return 0;
else if (index == 1) // Base case
return 1;
else // Reduction and recursive calls
return __________________;
}
```
a. fib(index - 1)
b. fib(index - 2)
c. fib(index - 1) + fib(index - 2)
d. fib(index - 2) + fib(index - 1)

c. fib(index - 1) + fib(index - 2)
d. fib(index - 2) + fib(index - 1)