What is the value stored in sum[4] after the following program is executed?

#include<stdio.h>
int max_num(int a,int b)
{
      if(a> b)
	  return a;
      return b;
}
int maximum_subarray_sum(int *arr, int len)
{
      int sum[len], idx;
      sum[0] = arr[0];
      for(idx = 1; idx < len; idx++)
	   sum[idx] = max_num(sum[idx - 1] + arr[idx], arr[idx]);
      int mx = sum[0];
      for(idx = 0; idx < len; idx++)
	  if(sum[idx] > mx)
	      mx =sum[idx];
      return mx;
}
int main()
{
      int arr[] = {-2, 14, 11, -13, 10, -5, 11, -6, 3, -5},len = 10;
      int ans = maximum_subarray_sum(arr, len);
      printf("%d",ans);
      return 0;
}

A. 28

B. 25

C. 22

D. 12

Answer: Option C