When you enter the supermarket, you see shelves full of goods. You walk between the shelves. You carry a shopping basket and put your food in it. You probably hear soft music as you walk. If you hear fast music, you walk quickly. The supermarket plays slow music. You walk slowly and have more time to buy things. Maybe you go to the meat department first. There is some meat on sale, and you want to find it. The manager of the supermarket knows where customers enter the meat department. The cheaper meat is at the end of the meat department, away from where the customers enter. You have to walk by all the expensive meat before you find the cheaper meat. Maybe you will buy some of the expensive meat instead of the meat on sale. The dairy (乳制品) department sells milk and milk products such as butter and cheese. Many customers like milk that has only a little butterfat in it. One store has three different jars of low fat milk. One says' 1 percent (1% )' fat on the container. The second says' 99 percent (99%) fat free'. The third says' Low Fat' in big letters and' 1%' in small letters. As you can see, all the milk has the same amount of fat. The milk is all the same. The amount of milk in each container is also the same. However in this store the three containers of milk don't cost the same. Maybe the customer will buy the milk that costs the most. Most of the food in supermarkets is very pleasing. It all says 'Buy me! ' to the customers. The expensive meat says 'Buy me!' as you walk by. The expensive milk jar says 'Buy me! I have less fat. ' The manager of the supermarket knows______ .