The man who brings my milk used to knock for his money for the week's milk while I was having breakfast on Saturday morning. Just lately he has been arriving before I get up. Staff shortages mean that four men are sharing five rounds, so he has to start earlier.  Delivering milk to people's homes is scarcely good business, especially when the customer may have a choice of two or three firms serving a single road. In spite of my local difficulties, however, labor troubles are not as sharp as a few years ago. There are enough men prepared to make an early morning for the sake of an open-air job with a fair measure of freedom. If they did stop calling, women would find it hard work to collect all the milk they need from self-service stores . Dairies are aware that stopping deliveries resulted in falling sales.  Marketing ideas have included introducing extra lines, in addition to dairy products, which the milkman can carry to increase turnover. Already they have taken over many rounds given up by bakeries. One dairyman said, "It wont' be long before the milkman delivers more bread that milk. " Some milkmen deliver potatoes, and it seems as if diversification will be limited only by the size of the vans.  So the milkman is likely to remain a familiar figure. Even the returnable bottle continues to be used. As long as it has a reasonable life--30 to 40 trips are usual-- the cost of collection and cleaning is worthwhile. Dairy firms continue to supply returnable milk bottles because they are   _  .
most economical in the long term the most durable form of container easy to clean and collect convenient for customers to return