单项选择题

Nearly every day, you and I deal with small coins and bank-notes (钞票). We need them for food and clothing. Whenever we want to buy something, we always have to pay for it with money. But what would we do when there were no metal coins and paper notes
Thousands of years ago, men did not have any money. The first men lived in caves (洞). Often they were hungry and cold. They didn’t need any money. But soon they found that some liked one kind of work better than another. But all of them had to eat and wear clothes. And everyone needed tools and weapons (武器). So they started to trade (做交易，进行贸易) with each other through buying things they needed or liked. People have used all kinds of "money". First, they traded with salt, animals’ tails and teeth... later they used a kind of metal named copper (铜). At last, people made money lighter. They made it out of paper.
We still use small coins and paper notes today. Could there be an even easier way to carry money Bank cards and Internet-banking are two such ways. ______ are used nowadays.