[LisonbeeQ6] Trace the following program and then list all of the possible outputs (just write the A/B/C/D text; no need for pids) that could be generated. (Assume that fork will always succeed.)

#include  #include  #include  int main() { pid_t pid1, pid2; pid1 = fork(); if (pid1 < 0) { fprintf(stderr, "Fork Failed"); return 1; } else if (pid1 == 0) { printf("A"); pid2 = fork(); if (pid2 < 0) { fprintf(stderr, "Fork Failed"); return 1; } else if (pid2 == 0) { printf("B"); } else { wait(NULL); printf("C"); } } else { printf("D"); } return 0; }