[LisonbeeQ5] Trace the program below, identify the values of the pids at lines A, B, C, D, E, and F. (Assume that the actual pid of Process 1 is 1502, Process 2 is 1505, and Process 3 is 1507. Also assume that fork will always succeed.)

#include  #include  #include  int main() { pid_t pid1, pid2, pid3; pid1 = fork(); if (pid1 < 0) { /* Error occurred */ fprintf(stderr, "Fork Failed"); return 1; } else if (pid1 == 0) { /* Process 2 */ pid2 = fork(); if (pid2 < 0) { /* Error occurred */ fprintf(stderr, "Fork Failed"); return 1; } else if (pid2 == 0) { /* Process 3 */ pid3 = getpid(); printf("pid2 = %d", pid2); /* A */ printf("pid3 = %d", pid3); /* B */ } else { /* Process 2 */ pid3 = getpid(); printf("pid2 = %d", pid2); /* C */ printf("pid3 = %d", pid3); /* D */ wait(NULL); } } else { /* Process 1 */ pid2 = getpid(); printf("pid1 = %d", pid1); /* E */ printf("pid2 = %d", pid2); /* F */ wait(NULL); } return 0; }