What is the output of the following code?

#include<stdio.h>
int recursive_binary_search(int *arr, int num, int lo, int hi)
{
      if(lo > hi)
        return -1;
      int mid = (lo + hi)/2;
      if(arr[mid] == num)
         return mid;
      else if(arr[mid] < num)
         lo = mid + 1;
      else
         hi = mid - 1;
      return recursive_binary_search(arr, num, lo, hi);
}
int main()
{
      int arr[8] = {1,2,3,4,5,6,7,8},num = 7,len = 8;
      int indx = recursive_binary_search(arr,num,0,len-1);
      printf("Index of %d is %d",num,indx);
      return 0;
}

A. Index of 7 is 4

B. Index of 7 is 5

C. Index of 7 is 6

D. Index of 7 is 7

Answer: Option C