Consider the following recursive implementation used to find the length of a string:

#include<stdio.h>
int recursive_get_len(char *s, int len)
{
      if(s[len] == 0)
        return 0;
      return ________;
}
int main()
{
      char *s = "abcdef";
      int len = recursive_get_len(s,0);
      printf("%d",len);
      return 0;
}

Which of the following lines should be inserted to complete the above code?

A. 1

B. len

C. recursive_get_len(s, len+1)

D. 1 + recursive_get_len(s, len+1)

Answer: Option D