Which of the following lines should be inserted to complete the following recursive implementation used to find the length of a linked list?

#include<stdio.h>
#include<stdlib.h>
struct Node
{
      int val;
      struct Node *next;
}*head;
int recursive_get_len(struct Node *current_node)
{
      if(current_node == 0)
        return 0;
      return _____;
}
int main()
{
      int arr[10] = {1,2,3,4,5}, n = 5, i;
      struct Node *temp, *newNode;
      head = (struct Node*)malloc(sizeof(struct Node));
      head->next = 0;
      temp = head;
      for(i=0; i<n; i++)
      {
          newNode = (struct Node*)malloc(sizeof(struct Node));
          newNode->val = arr[i];
          newNode->next = 0;
          temp->next = newNode;
          temp = temp->next;
      }
      int len = recursive_get_len(head->next);
      printf("%d",len);
      return 0;
}

A. recursive_get_len(current_node)

B. 1 + recursive_get_len(current_node)

C. recursive_get_len(current_node->next)

D. 1 + recursive_get_len(current_node->next)

Answer: Option D