阅读理解 　　Money is used for buying or selling goods, for measuring value and for storing wealth. Almost every society now has a money economy based on coins and bills of one kind or another. However, this has not always been true. In primitive societies a system of barter was 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(确切的) 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, feathers, skulls, salt, elephant tusks, and tobacco had all been used. Precious metals gradually took over because, when made into coins, they were portable, durable(耐用的), recognizable, and divisible(可分的) into larger and smaller units of value. 　　A coin is a piece of metal, usually disc－shaped, which bears letters, designs or numbers showing its value. Until the eighteenth and nineteenth 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, aluminum, nickel, lead, zinc, 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 United States, many places, especially filling stations, will not accept cash at night for security reasons. 1．Barter here means ________. [　　] A．exchanging goods for money B．exchanging a sheep for anything in the market C．exchanging goods for goods D．exchanging money for goods 2．Why were precious metals gradually used for making coins? [　　] A．Because they were durable and portable. ' B．Because they were divisible. C．Because they were recognizable. D．All of the above. 3．Coins were given value according to the exact amount of metals contained in them ________. [　　] A．before the eighteenth and nineteenth centuries B．after the eighteenth and nineteenth centuries C．during the eighteenth and nineteenth centuries D．between the eighteenth and nineteenth centuries 4．“Promises to pay” means ________. [　　] A．possibilities to pay B．necessities to pay C．obligations to pay D．opportunities to pay 5．A world without any money in the form of coins and paper is ________. [　　] A．suitable B．possible C．necessary D．avoidable