【答案解析】[听力原文] In man's early progress toward civilization, there were many great steps forward——the domestication of animals, the invention of the wheel, the development of writing, the use of money, the growth of commerce and cities~ But the most important step of all was the beginning of agriculture. If man had remained a hunter, none of the rest of his accomplishments would have been possible. We do not know how agriculture began. It is probable that the first crops that were grown for food were grains, such as wheat, barley, rye, oats, and rice. From these grains, one of man's most important foods——bread--is made. Even at the beginning of historical times——that is, the period in which we have written records——the making of bread was well known. All the details of life in ancient Egypt, including the making of bread, are shown in wall paintings. In the most ancient records that we have, there are hundreds of references to the raising of wheat and to the making of bread.