【正确答案】 D

【答案解析】[听力原文] Moderator: Welcome to 'Science World'. Today we have Dr. Michael Hudson, Chief of the Department of Life Science in Boston University. It is estimated that over 99 percent of all species that ever existed have become extinct. What causes extinction? Dr. Hudson: Well, when a species is no longer adapted to a changed environment, it may perish. The exact causes of a species' death vary from situation to situation. Rapid ecological change may render an environment hostile to a species. For example, temperatures may change and a species may not be able to adapt. Food resources may be affected by environmental changes, which will then cause problems for a species requiring these resources. Other species may become better adapted to an environment, resulting in competition and, ultimately, in the death of a species. The fossil record reveals that extinction has occurred throughout the history of Earth. Recent analyses have also revealed that on some occasions many species become extinct at the same time—a mass extinction. One of the best-known examples of mass extinction occurred 65 million years ago with the demise of dinosaurs and many other forms of life. Perhaps the largest mass extinction was the one that occurred 225 million years ago, when approximately 95 percent of all species died. Mass extinctions can be caused by a relatively rapid change in the environment and can be worsened by the close interrelationship of many species. One interesting and controversial finding is that extinctions during the past 250 million years have tended to be more intense every 26 million years. This periodic extinction might be due to intersection of the Earth's orbit with a cloud of comets, but this theory is purely speculative. Some researchers have also speculated that extinction may be random. That is, certain species may be eliminated and others may survive for no particular reason. A species' survival may have nothing to do with its ability or inability to adapt. If so, some of evolutionary history may reflect a sequence of essentially random events. Q: What does Dr. Hudson say regarding the vast majority of species in Earth's history at the beginning of the lecture? 解题思路：四个选项均以they开头，对其进行描述，分别表示四个方面：形态、适应能力、对环境的影响以及是否存在。听录音时注意听清they的指代对象，抓住每项所描述的某个方面的内容。 在讲座的开始部分，主持人询问“超过99%的物种已经灭绝的原因”，这里“超过99%的物种”即对应问题中的“绝大部分物种”。赫德森博士接下来对它们灭绝的原因做了解释。由此可知它们都已经灭绝了，不复存在，故选D。有关形态的内容讲座中未提及，排除A；B项和C项则与讲座内容不符。

【正确答案】 A

【答案解析】[听力原文] Q: What does the evidence from fossils suggest? 解题思路：四个选项均出现了有关“灭绝”(extinction、extinctions和extinct)的词汇，考查的内容与物种或生物灭绝有关。听录音时注意抓住各项的关键信息(occurred...throughout Earth's history, generally been massive, only one mass extinction和dinosaurs became extinct much earlier)。 在提到化石证据时，赫德森博士说：“纵观地球的整个历史，灭绝从未停止过。”A项是对讲座内容的同义转述，为正确答案。B项表述过于绝对，不符合讲座内容，应排除；历史上曾有过多次大规模生物灭绝事件发生，规模最大的一次发生在2亿2500万年前，因此排除C；对于恐龙灭绝的时间讲座中并未提及，排除D。

【正确答案】 B

【答案解析】[听力原文] Q: What can we learn about the 'interesting and controversial' finding? 解题思路：四个选项的主语各不相同，需要逐一提取各项的重点信息：灭绝事件的加剧、周期性灭绝的原因、是否被验证以及生存能力与适应能力的关系。听录音时应有针对性地留意这些重点信息。 在讲座的结尾部分，赫德森博士这样论述该发现“在过去2亿5000万年间发生的灭绝事件每隔2600万年就会加剧一次。这种周期性的灭绝可能是由于地球轨道与彗星星云的交汇，但这个理论只是一种猜想”。由此可知B项符合文意，故为答案。A项中的时间信息错误，排除；C项内容讲座中未提及，应排除；D项内容与该发现无关，也应排除。