【正确答案】 B

【答案解析】[听力原文] Your reading for today touched on dinosaur fossils from the Mesozoic era, which ended about 65 million years ago. Today we will be discussing the sauropods. They were an extremely successful kind of dinosaur. There's evidence of sauropods in the fossil record for an unusually long time, over one hundred million years. So, why were sauropods so successful? Biologically speaking, sauropods shouldn't have been successful. Large animals like elephants, say, they require much more food and energy and what's typically is that they usually have fewer offspring than smaller animals. This makes maintaining a population harder. The largest animals today don't live on land but in the ocean where food is easier to find. A blue whale, for instance, can eat up to 8,000 pounds of food a day. And they give birth only once every few years. We also know that body heat, that...well, large animals can't easily get rid of excess body heat. But for an oceangoing whale, that's not a problem. For a 100-ton land animal, it can be. For years, we have assumed it was the abundant plant life of the Mesozoic that allowed these giants to thrive. However, we now know that since oxygen levels were much lower in the Mesozoic than we assumed, there was much less plant life for sauropods to eat than we thought. So now, well, we are trying to understand the biology of sauropods, comparing their fossils to get a better idea of how they live. What we've found is that sauropods were experts at conserving energy. They had enormous stomach capacity, the ability to digest food over a long period, converting it to energy at a slower pace, saving it for later. But you know there's always some guesswork when studying extinct animals. We guess the hypothesis by looking for evidence to support it. Then some questions are answered, which may lead to new questions. Anyhow, I think they are useful in proving the truth. For example, we know sauropods couldn't chew food. Their skulls show they had no chewing muscles. Lots of modern animals, like birds, also can't chew food. But modern animals have an interesting aid for digesting food. They swallow stones, stones that are used to help grind up the food before it's actually digested in the stomach. Now, sauropod fossils are commonly found with smooth stones. But there are studies which now make us not quite sure what these sauropods' stones were used for. It could be they served no real purpose. Other researchers speculate that sauropods swalloed these stones as a source of some the minerals they needed, such as calcium. So the original hypothesis, even though it hasn't been supported, has helped us to make new hypotheses, which may eventually lead to the answer. Compared to small animals, what disadvantages do large animals typically have? 本录音前两题选项中重复出现的large animals和in the Mesoz01c era，以及food，energy和populations表明，录音可能与某个时期的大型动物有关，可能涉及当时一些动物的数量或觅食、运动方式。选项均为描述large animals的句子，其中的require more food, have fewer offspring, need more energy和staying warm可知，本题可能考查大型动物的生存特点。录音中提到，与小型的动物相比，大型动物需要更多的食物和能量，而且典型的是通常他们的后代更少(fewer offspring)，故答案为B。

【正确答案】 D

【答案解析】[听力原文] According to the professor, what recent finding about the Mesozoic era challenges an earlier belief? 选项中重复出现的in the Mesozoic era和than previously believe，以及populations和oxygen/ocean levels表明，本题可能考查某个时期所发生的变化，可能涉及地理环境和动植物的数量。录音中提到，很多年以来我们都认为是中生代丰富的植物群(abundant plant life)使这些巨型动物得以存活，现在却发现由于中生代时期的氧气含量比我们假定的低，蜥脚类恐龙可吃的食物比我们认为的要少。D是对该发现的概括，故为答案。