What is the time complexity of the following recursive implementation used to find the length of the string?

[answerhappygod]

#include<stdio.h>
int recursive_get_len(char *s, int len)
{
if(s[len] == 0)
return 0;
return 1 + recursive_get_len(s, len+1);
}
int main()
{
char *s = "abcdef";
int len = recursive_get_len(s,0);
printf("%d",len);
return 0;
}
a) O(1)
b) O(n)
c) O(n2)
d) O(n3)