Mr Smith is introducing some changes of buying.

He says: 50 years ago, there weren't many shops there, people must use some tickets to buy some food, clothes and tools. But at that time, tickets were not enough for each person. They must think about it carefully then spent it to buy something. People just ate a little meat one month and dressed little clothes for each one. They must buy something from one village to another village, even around the city.

His students: What about now?

He says: Now, there are many shops here, people except use money to buy, they can also use card. They don't worry about the commodities are not enough for each person. People can eat more food and dress many beautiful clothes, use many tools and read many books now. Besides, they can buy something from one city to another city, they also can buy them on phone, TV and Internet.