Money is used for buying or selling goods, for measuring value and for storing wealth. However, in primitive societies a system of barterwas used. Barter was a system of direct exchange of goods. Somebody could exchange a sheep, for example, for anything in the market place that he or she considered to be of equal value. Barter, however, was a very unsatisfactory system because people’s precise needs seldom met. People needed a more practical system of exchange, and various money systems developed based on goods that the members of a society recognized as having value. Cattle, grain, teeth, shells, salt, and tobacco had all been used. Precious metals gradually took over because, when made into coins, they were potable, durable, recognizable, and divisible into larger and smaller units of value.A coin is a piece of metal, usually disc-shaped, which bears lettering, designs or numbers showing its value. Until the 18th and 19th centuries, coins were given monetary worth based on the exact amount of metal contained in them, but most modern coins are based on face value -----the value that the governments choose to give them, which doesn’t show the actual metal content. Coins have been made of gold, silver, copper, plastic and in China even from tea leaves. Most governments now issue paper money in the form of bills, which are really “promises to pay”. Paper money is obviously easier to handle and much more convenient in the modern world. Checks and credit cards are being used increasingly, and it is possible to imagine a world where “money” in the form of coins and paper currency will no longer be used. Even today, in the U.S., many places, especially filling stations will not accept cash at night for security reasons. （1）“Barter” (in Line 2, Paragraph 1) here means _____.