Money is something we all take for (1)_-_ in our lives. Some of us may wish we had more of it but we all recognize it when we see it, whether in the form of coins, notes or (2)_--. It is difficult to imagine how people managed without money. In the earliest periods of human history, people used to exchange goods (3)-. They would exchange things they had plenty of for things that they were in need of. For example, they might offer food for tools. This method of exchange, which is known as barter, has many (4)---. Certain goods may be difficult to carry, they may not last long, or may be impossible to divide into (5)-- units. It can also be difficult to know the worth of something compared with other goods.