#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/wait.h>
 
int main() {
    printf("A\n");  // 主行程：印 A（一定最先出現）
 
    if (fork() == 0) {  // fork 一個子行程 P1
 
        printf("B\n");  // P1 印出 B
 
        if (fork() == 0) {  // P1 fork 出 P2
 
            printf("C\n");  // P2 印 C
        } else {
            wait(NULL);      // P1 等 P2 結束
            printf("D\n");   // P1 印 D
        }
 
    } else {
 
        printf("E\n");  // 主行程印 E
        wait(NULL);     // 等 P1 結束
    }
 
    return 0;
}

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