题目： Transportation and Economic Change in the Nineteenth-Century       Between 1820 and 1860,the American economy entered a new stage of develop...

TF阅读真题第838篇Germanic Invasions of the Roman Empire

TF阅读真题第839篇Money in the European Middle Ages

Life on Mars Astronomers strongly suspect that Mars currently has no liquid water, diminishing the chances for life there now. But running water and a denser atmosphere in the pas...

TF阅读真题第844篇Climate Change and Species Distribution

TF阅读真题第840篇Rogue Planets

Extraterrestrial lmpact and Megafauna Extinctions     About 13,000 years ago, near the end of a period called the Pleistocene, North America was populated by megafauna (...

TF阅读真题第815篇Archaeopteryx and Bird Evolution

TF阅读真题第824篇Asphalt

Degradation and Erosion of Soil Land without soil can support only very small primitive plants such as lichens and mosses that can cling onto a rock surface. The rest of the worl...