TOEFL Reading: ETS-TOEFL阅读机经 - 0F7K14R75MD355ZGL$

During the last ice age, human hunters pursued large animals across Beringia, a land whose climatic characteristics have been in dispute. A. Strong evidence indicates that large mammals like mammoth and bison survived in the harsh ice-age Beringian landscape. B. Carnivores such as the saber-tooth cat were primarily responsible for the disappearance of the largest of the grazing animals, but the harsh winters caused some grazers to die of starvation. C. The discovery that grasses, sedges, and mosses survived under the thick ash from a large volcanic eruption proved that the ice-age Beringian plant cover was extremely resistant to climatic extremes. D. Beringian mammals crossed easily from northeastern Asia to Alaska across the Bering Land Bridge, though there are indications that they usually went back to Asia for the brief, but warm, summers. E. Analysis of ice-age sediments uncovered very small amounts of pollen, suggesting that Beringia lacked the quantity of vegetation needed to support large herds of mammals. F. Recent discoveries suggested that shallow-rooted plants created a fairly continuous cover over ice-age Beringia, though the cover most likely was variable and uncertain in any one location.