来源：沪江听写酷 2014-11-19 20:30
Questions 47-50 Listen to part of a lecture from the American civilization course. In the late 1400s, when Christopher Columbus returned to Spain from the western hemisphere, he brought with him a sample of what the native Americans called maze, or, as we call it more often today, corn. The corn that Columbus introduced to Europe was the distant descendant of a grass native to Mexico. The peoples of the Americas probably started to domesticate this grass as early as 5000BC. After about a thousand years, they had developed a highly productive strands of corn which later became the basis for the great pre-Columbian civilizations. Figuratively speaking, both the cities of the Incas and the temples of the Mayas were built on corn. Domesticated corn and the people who cultivated it developed together. Without humans to care for it, domesticated corn could not survive. The kernels are crowed together beneath the strong protected husk and silk. And the young corn shoot is not strong enough to break through the husk on its own. If people did not strip away the husk and plant individual kernels, the corn would die out.