What is the output of this program

#include<stdio.h>
#include<pthread.h>
 
void *fun_t(void *arg);
void *fun_t(void *arg)
{
    pthread_exit("Bye");    
}
int main()
{
    pthread_t pt;
    void *res_t;
    int ret;        
    ret = pthread_join(pt,&res_t);
    printf("%d\n",ret);
    return 0;
}

A. 0

B. -1

C. 2

D. 3

Answer: Option D