Which of the following can be the base case for the recursive implementation used to find the length of linked list?

#include<stdio.h>
#include<stdlib.h>
struct Node
{
      int val;
      struct Node *next;
}*head;
int get_len()
{
      struct Node *temp = head->next;
      int len = 0;
      while(temp != 0)
      {
          len++;
          temp = temp->next;
      }
      return len;
}
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;
      int len = get_len();
      printf("%d",len);
      return 0;
}

A. if(current_node == 0) return 1

B. if(current_node->next == 0) return 1

C. if(current_node->next == 0) return 0

D. if(current_node == 0) return 0

Answer: Option D