What is the time complexity of the following recursive implementation of linear search?

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

A. O(1)

B. O(n)

C. O(n²)

D. O(n³)

Answer: Option B