answer: Miss Yang has not been sure of two phrases. I'm sorry and excuse me. Mr. Smith explains how to use them correctly.
documents: #Person1#: Mr. Smith, may I ask you a question?
  #Person2#: Yes, go ahead, please.
  #Person1#: For quite a long time, I've not been sure of two phrases. I'm sorry and excuse me. It seems that they have exactly the same meaning when we put them into Chinese. Could you tell me how to use them correctly?
  #Person2#: Alright. In fact, there are a lot of differences between the two. I'd better show you some examples. Suppose you are chatting with someone, if you'll use a phrase as a polite way of indicating that you are about to leave or that you are about to stop it.
  #Person1#: I am sorry?
  #Person2#: No, we say, excuse me or excuse me, please. And excuse me is also used when we are going to interrupt someone who is speaking or... ... 
  #Person1#: Excuse me, Mr. Smith.
  #Person2#: Very good, Miss Yang. What are you going to say?
  #Person1#: If we knock into somebody by chance, when pushing our way out, we should then say sorry or I'm so sorry?
  #Person2#: You learn so fast.