Passage 4
When Columbus reached the New World, corn was the most widely grown plant in the Americas. A study by an American professor who was an important figure in the field of American history, has shown that this plant's range extended from what is now southern Canada to lower South America. At that time some tribes cultivated it at sea level, others at elevation of more 11,000 feet. It could grow in almost every corner of Americas simply because its strong flexibility to various weathers.
“Columbus had no way of knowing that corn was far more valuable than the spices and gold he had hoped to find,” said Frances B. King, a professor at a university of Pittsburgh. At Columbus time, corn was rather strong but short. Through human intervention, this plant has developed into several hundred races, or varieties. Their heights vary from 2 to 12 feet, and their maturity ranges from little more than 2 months to almost a year. Their ears vary not only in color, but also in size.
Unlike other cereals, corn bears little resemblance to its wild ancestors. In fact, it differs from the appearance of its immediate ancestors more than any other cultivated plant known. From humble origins as a lowland grass, corn developed into western world's important grain, which is now widely used to feed cattle, or domestic animals and even human beings. As its high yields allowed communities to grow far beyond what early agriculture could feed, most scientists viewed corn as having largely fueled pre-Columbian growth and civilization. Now, new findings are greatly altering researchers' notions about the time when corn revolution occurred. The findings were obtained through several years' research and field investigation by a great number of scientists. New dates for its emergence from Mesoamerica do not support the widely held view. The evidence now suggests that the signs of corn in Americas can date back 5,500 years at least.
The first paragraph states that corn ________.
由第一段中“corn was the most widely grown plant in the Americas”可知D项正确。
The second paragraph implies that ________.
作者在文中第二段提到“Columbus had no way of knowing that corn was far more valuable than the spices and gold he had hoped to find”，也就是说，玉米比哥伦布想要找到的香料和黄金更有价值。
According to the passage, some varieties of corn can ________.
第二段中提到“their maturity ranges from little more than 2 months to almost a year”由此可见玉米的成熟期从只有2个月至几乎12个月。
Corn helped the early communities to grow because ________.
由最后一段中“As its high yields allowed communities to grow far beyond…having largely fueled pre-Columbian growth and civilization.”可知，科学家们认为玉米的高产量推动了早期社会与文明的发展。
The widely held view was challenged by ________.
由文章最后可知，人们现有的观点受到了“New dates for its emergence from Mesoamerica”的挑战，也就是关于玉米的新发现。