根据下列短文内容，在短文后的空格处填上一个恰当的词，使短文完整、通顺。
   We usually use ____  kinds of money. One kind is money made of paper and the other kind is money made of metal.  But in the past people used many things ____ of money. Some countries used salt, tea or stones. Other countries even used some animals. Today people in some places in the world ____  do not use paper money all the time.
   On the island of Yap, people use the ____  money in the world —Yap stones . These are round, white stones ____ a hole in the middle. The Yap stones do not ____  from this island. The Yap men have to go to the islands over 600 kilometres away to get ____   
Rich people do not carry the heavy Yap stones. Servants  ____  the rich. Today people on the island of Yap use paper money for everyday shopping. But for other things they still ____ Yap stones to ____  money.