用一句话总结Text A 第一段的中心思想。请用英语回答。 Text A 第一段原文: Corn and potatoes are two vegetables from the New World which are now part of the world's diet. There is hardly a corner of the world where these vegetables are not grown and eaten. Ironically, until the discovery of the Americas the world had not known of these two crops. These food items, however, were first harvested by the native Indians who lived on the land and were later introduced into Europe by the early explorers. For example,the potato, was not introduced into North America until 1621 when it was brought to Virginia from Bermuda.