TOEFL Listening: TPO-TOEFL阅读TPO - 08338EO2C8CT30RCN$

Recent evidence favors a rival to the long-standing theory that the Americas were colonized 11,000-12,000 years ago by people migrating south from Beringia along a midcontinental ice-free corridor. A. Evidence that an ice-free corridor between two ice sheets developed when the continental ice first began to melt came primarily from radiocarbon dating. B. There is growing support for the theory that migration took place much earlier, by sea, following a coastal route along Alaska and down the northwest coast. C. Recent geologic evidence indicates that contrary to what had been believed, substantial areas along the coast were free of ice as early as 16,000 years ago. D. Research now indicates that the parts of the inner continental shelf that remained covered with ice were colonized by a variety of early human groups well adapted to living in extremely cold environments. E. There is evidence suggesting that areas along the coast may have contained enough food resources between 13,000 and 14,000 years ago to have made human colonization possible. F. Even though the northern part of the continent allowed for a more varied economy, several early human groups quickly moved south.