answer: #Person1# explains to #Person2# the difference between two coins made in different periods of the Tang Dynasty and the methods to tell a fake ancient coin. #Person1# also introduces the existence of different coins made by various foreign tribes in different periods.
documents: #Person1#: Look, here're two coins named Kai Yuan Tong Bao, the sort of coin made in memory of the founding of a new dynasty. These two coins were made in different periods of the Tang Dynasty.
  #Person2#: How can you tell the difference? From what I see, they look almost the same.
  #Person1#: The one made in the early Tang period is bigger and has more characters on it, while the one with smaller and elegant characters was made in late Tang period. Look carefully, and tell me if you see the difference now.
  #Person2#: Yes, they are different! But it's too professional. What I need is just being able to tell the real from the fake. Do you know any method we can use to tell a fake ancient coin?
  #Person1#: Various methods were used in history to produce fake coins. We usually send the coin to an authorized unit to have it tested by experts with special machines. We can judge it with naked eyes.
  #Person2#: I see. By the way, China was more than once ruled by foreign tribes in history. Did they issue their own coins in China?
  #Person1#: Certainly, they did. Liao Coins and Song Coins, for example, coexisted in circulation during the Southern Song and Yuan period some 800 -1000 years ago. The Liao Coins look plain and bold in style, just like the characteristics of the Mongolian tribe. Let me look for one and show you.
  #Person2#: If you happen to find one, please bargain with the owner for it. I'd like to have one. It's interesting to see the integration of the Han and Mongolian cultures on this small piece of metal.