In the American colonies there was little money．England did not supply the colonies with coins and it did not allow the colonies to make their own coins．Only the Massachusetts Bay Colony received permission for a short period in 1652 to make several kinds of silver coins．England wanted to keep money out of America as a means of controlling trade：America was forced to trade only with England if it did not have the money to buy products from other countries． The result during the pre-revolutionary period was that the colonists used various goods in place of money：beaver furs，Indian wampum，and tobacco leaves were all commonly used as substitutes(代替物)for money．The colonists also made use of any foreign coins they could obtain．Dutch，Spanish，French，and English coins were all in use in the American colonies．
Individual states and the Continental Congress issued paper money．S0 much of this paper money was printed that by the end of the Revolutionary War it was virtually worthless．As a result，trade in goods and the use of foreign coins were still common during this period．
By the time the Revolutionary War had been won by the American colonists，the monetary(货币的)system was in a state of total confusion．To change this situation，the new Constitution of the United States，approved in 1789，allowed only Congress to issue money．The individual states could no longer have their own money supply．A few years later，the Coinage Act of 1792 made the dollar the official currency of the United States and put the country on a bimetallic(双金属的)standard．In this bimetallic system，both go1d and silver were legal money，and the rate of exchange of silver to gold was fixed by the government at sixteen to one．
28. The reason why England kept money out of America was that______
A. American colonies could have their own coins
B. America had to trade only with England
C. the colonists wanted to save the money for their own country
D. too much paper money in use would lead to the decrease of value
29. What happened to the American monetary system during the Revolutionary War?
A. Individual states were not allowed to issue money．
B. The Continental Congress issued g01d and silver coins．
C. American money replaced trade-in goods and foreign coins.
D. So much paper money was in use that it almost lost its value at last：
30. According to the passage，under the new US Constitution____.
A. only the US Congress could issue money
B. the dollar was made the official currency of the US
C. the US officially went on a bimetallic monetary system
D. various state governments，including Massachusetts，could issue money
31. This passage mainly discusses _____.
A. the American monetary system during the 17th and 18th centuries
B. the English monetary policies in American colonies
C. the effect of the Revolutionary War on American money
D. American money from past to present