at once and

例句：

1. 1. I'll be there at once when you need me.
   你需要我的时候我会立刻到。
2. 2. He arrived at once after the meeting ended.
   会议结束后他立刻到达了。
3. 3.She was so excited that she couldn't wait to tell her friends about it.
   她太兴奋了，迫不及待地要告诉她的朋友们。