Greetings in Passing
It is polite to greet a person you know. However, you don't always have time to stop and have a conversation. Just remember to smile as you say hello. A small wave is also polite. Sometimes you pass the same person a second time on the same day. You can say "hello again" or just smile.
跟认识的人打招呼是有礼貌的体现，但是你们并不会每次都有时间停下来谈谈。只要记住说“你好”的时候带上微笑就行了，另外轻轻招手也会显得很礼貌。有些时候你可能在同一天再次碰到这个人，那时你可以说"hello again"，或者仅用微笑示意。
Tips
•Slow down to greet someone you know. You don't have to stop what you are doing (walking, working, shopping).
放慢动作来同认识的人打招呼，不必停下（脚步，工作，购物）。
•Say an appropriate form of hello.
选择正确的打招呼方式。
•Smile and wave.
微笑+挥手。