Unit 5 Launching Your Career 单元限时小卷-【高中必刷题】2023-2024学年新教材高中英语选择性必修第四册同步课件（人教版2019）

03 单元限时小卷 建议用时：50分钟 1 [陕西西安2022高二期末] The lack of clues left behind by ancient Americans has made it difficult for researchers to determine precisely when humans first arrived on the continent. However, it has always been believed to be about 13,000 years ago. Now, evidence from the Chiquihuite Cave in Zacatecas, Central Mexico, seems to suggest that prehistoric humans may have been living in North America as early as 30,000 years ago. Dr Ciprian Ardelean, of the Autonomous University of Zacatecas, who led the groundbreaking research, first became aware of the cave in May 2010. Getting to the cave located 2,740 metres above sea level required a 45-minute truck ride to the base and an uphill climb over a rough terrain. However, Dr Ardelean and his team found enough clues to make the difficult journey three additional times—in 2012, 2016 and 2017. 刷阅读理解 2 The archaeologists' efforts revealed many artefacts including over 1,900 stone tools from multiple layers of the cave. The scientists found that most of the tools were between 13,000 and 16,000 years old. However, 239 artefacts unearthed from the deepest layer of the cave dated back an astonishing 30,000 years! While the genetic material gained in the cave was only plant and animal DNA, the team did find evidence of sulphur, potassium and zinc elements that could indicate human activities such as killing animals. Dr Ardelean says the absence of human DNA confirms that the early people visited the cave for short periods of time. 刷阅读理解 3 The researchers are unsure of the ancient humans' origins or the path they took to get to America. They guess the groups were tribes （部落） who moved from place to place and went extinct at some point during their migrations. Dr Ardelean says, “We don't know who they were, where they came from or where they went. They're a complete enigma. We falsely assume that the native populations in the Americas today are direct descendants from the earliest Americans, but now we