听力原文： Ask a typical American to name the biggest business in the United States, and

youre likely to get an answer such as "banking" or "automobile manufacturing". Neither is correct. The right reply is surprisingly obvious when you consider what 235 million people do at least three times a day — they eat. The food business is by far Americas largest enterprise. And an increasingly large part of that business comes not from growing the food or selling it in Americas stores, but from distributing it. In every corner of the nation, the distribution network works 24 hours a day, moving food by truck, train, ship and frequently by airplane. It has been estimated that there are more than 135,000 different grocery products, ranging from bottles of fresh milk to cans of cooked fish, constantly being moved through the system. Food in America is moved by a network that is so complicated that no one has ever been able to figure it out. There is no central governmental supervision of the system, although scores of government agencies at the federal, state and local levels have responsibilities for regulating the safety, shipment and sale of food. The system would seem to be one of complete disorder, and to the outsider who examines it, it is. But it works with amazing efficiency. Questions 19 to 21 are based on the passage you have just heard. 19. According to the passage, which is the biggest business in America？ 20. How many different grocery products are being sold in America？ 21. According to the passage, what is the increasingly large part of the business？20．

A．135,000.

B．350000

C．515,000.

D．531000