once you arrive和once you reach都对吗?

once you arrive和once you reach都对吗? 英语翻译once you arrive at the Expo site. once! once once Once once Once once once once When you arrive at there, please call me at once . 这句话错误在哪 Time can you back once in?once Please write to me at once when you arrive .(同义句)Please write to me at once when you arrive .(改为同义句)Please write to me ___ ___ ____ you arrive. once again和once more的区别? please write to me at once when you arrive改为同义句：please write to me 〈三个词〉you arrive Please write to me at once when you arrive (改为疑问句）谢谢了,大神帮忙啊 you are only young once