Consider the program below, concurrent program with multiple threads: volatile int counter = 50; void *worker (void*arg) { counter--; return NULL; } int main(int argc, char*argv[]) { pthread_t p1, p2; pthread_create (&p1, NULL, worker, NULL) ; pthread_create (&p2, NULL, worker, NULL); } pthread_join (p1, NULL); pthread_join (p2, NULL); printf("%d ", counter); return 0; Assuming pthread_create () and pthread_join () all work as expected (i.e., they don't return an error), select all possible outputs? 0 49 48 51 50