An old man walked slowly into a restaurant with his cane(拐杖).His old jacket and shoes made him unusual that day.

    A young waitress named Mary watched him move towards a table by the window.She ran over to him,and said with smile,“Here,sir.Let me give you a hand."

    Without saying a word,he gave her a smile. She pulled the chair out from the table and helped him sit down. Then she put his cane against the table where he could reach ithimself. In a soft, clear voice he said,"Thank you." "You're welome, sir," she replied. I'll be back in a moment, and if you need anything, just wave(挥手) at me!"

    After he had finished a good meal,Mary brought him the change. She handed him his cane, and walked to the front door. Holding the door open for him, she said,“Come back and see us, sir! ”The old man turned around and smiled.

    When Mary went to clean his table, she was shocked. Under the plate, she found a business card, a 100—dollar and a note.The note said.

    “Dear Mary, I respect you very much, and you respect yourself, too. It shows the way you treat others. You have found the secret of happiness."

    In fact,the old man was the owner of the restaurant. That was the first time that she, or any of his waitresses, had seen him.

下面是四种应用文的部分摘录，请根据应用文的语言特点，找出每种应用文的不得体之处并进行修改。

①校团委会决定5月10日下午在学校体育馆举办首届体育节活动。欢迎各位同学莅临现场，积极参加。(校团委会通知)

②大家好，欢迎各位来到赵县参观“千年彩虹”赵州桥。我是导游，希望大家尊称我“小李”，我将竭诚为大家服务。(导游词)

③各位来宾、各位校友，大家好。今天是我校50周年校庆日，学校的图书馆、校史馆、办公楼全部开放。(广播稿)

①       将____      改为____　         ②将____　　　改为____　 

②       将____　　　改为____　      

③      

当A、B两点中有一点在原点时，不妨设点A在原点，

如图1，|AB|=|OB|=|b|=|a﹣b|；

当A、B两点都不在原点时，

如图2，点A、B都在原点的右边

|AB|=|OB|﹣|OA|=|b|﹣|a|=b﹣a=|a﹣b|；

如图3，点A、B都在原点的左边，

|AB|=|OB|﹣|OA|=|b|﹣|a|=﹣b﹣（﹣a）=|a﹣b|；

如图4，点A、B在原点的两边，

|AB|=|OB|+|OA|=|a|+|b|=a+（﹣b）=|a﹣b|；

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