A、A narrow strip of land. B、A manufacture bridge. C、A narrow strait. D、An island. A推理题。由原文可知，在哥伦布发现新大陆的几千年前，印第安人穿过连接阿拉斯加和西伯利亚的一块

Good morning, everyone. Welcome to the lecture. Today I’d like to talk about the American Indians with you. They are considered a people in crisis now. However, Indians were the first Americans. They lived in North America long before the continent was settled by Europeans. Through a long and difficult struggle that continues to this day, the Indians have striven to preserve their traditions, their religion, and their culture. In this they have shown great determination, continuing to hunt and fish or to manage small farms just as their ancestors did. But compared to other Americans, most Indians are poor. And this is their problem.(23)Conditions which favored the old life are gone forever, and yet many Indians are unable to adopt the white man’s ways. Now some of them are in trouble with the law. How did this trouble start? Who are the Indians? Where did they come from? Where do the live today? Why is it so difficult for them to assimilate? Let’s discuss these issues together.
    First of all, let’s look at the origin of the American Indians. The American Indians are of Asian ancestry.(24)Thousands of years before Columbus came to the New World, they entered North America by crossing a narrow strip of land that one connected Alaska and Siberia. Ancient geological changes raised the level of the oceans covering this natural bridge with water. Today this place is called the Bering Strait. At its narrowest point, the Strait is only 56 miles wide. In ancient times as today, a crossing there, even by primitive boat, must have been comparatively easy.
    The migrants entered a new world in which there were no people at all. But there were forests where many animals to be hunt, and nuts, roots, and berries to be gathered. Living comfortably on this food supply, the newcomers spread out. Some moved south into Central and South America. Others traveled east of the Atlantic Ocean. These migrations were gradual, probably taking thousands of years. Eventually, the people who became the American Indians had spread across North America.
    Secondly, the development of American Indians in this continent. These migrants contained groups of quite different cultural ancestry. This is evident in the variety of languages they spoke.(25)There are at least 200 separate Indian languages in North America, each with its own grammar and vocabulary. And none is related in any way to English or any other European language.
    The regions of North America where the newcomers lived varied greatly in climate and food supply. In the plains and eastern forests where resources were plentiful, the Indians hunted and fished. In the dry Southwest, they farmed. These regional differences explain the richness and variety of Indian culture: dissimilar economics produced quite different systems of society.
    For instance, many Indians of the Southwest, such as the Hopi and the Zuni, were village Indians. They built mud brick houses and developed agriculture. Many of them learned to irrigate: others became expert dry farmer. They grew beans, corn, and other vegetables. They made baskets, raised and wove cotton, and made beautiful pottery.
Now listen to the following recording and answer questions 23 to 25.
23. According to the lecture, what is the main reason that the American Indians are in crisis now?
24. According to the lecture, what was the geological status of the Bering Strait in thousands years ago?
25. How many languages exist in North America, which have their own grammar and vocabulary?