【正文】 he United States don39。new or improved,39。t well supported either. You know that mound at Pueblo Alto? It contains lots of other materials besides broken pots, stuff you wouldn39。t there more spilled maize on the floor? Why aren39。t have been residential. Second, the idea that the great houses were used to store grain maize 。t rapidly growing. These growth rings are evidence that dinosaurs stopped growing or grew more slowly during cooler periods. This pattern of periodic growth, you know, rapid growth followed by no growth or slow growth, and then rapid growth again, is characteristic of animals that are not endotherms. Animals that maintain a constant body temperature yearround as true endotherms do grow rapidly even when the environment bees cool. TPO 5Reading As early as the twelfth century ., the settlements of Chaco Canyon in New Mexico in the American Southwest were notable for their great houses, massive stone buildings that contain hundreds of rooms and often stand three or four stories high. Archaeologists have been trying to determine how the buildings were used. While there is still no universally agreed upon explanation, there are three peting theories. One theory holds that the Chaco structures were purely residential, with each housing hundreds of people. Supporters of this theory have interpreted Chaco great houses as earlier versions of the architecture seen in more recent Southwest societies. In particular, the Chaco houses appear strikingly similar to the large, wellknown apartment buildings at Taos, New Mexico, in which many people have been living for centuries. A second theory contends that the Chaco structures were used to store food supplies. One of the main crops of the Chaco people was grain maize, which could be stored for long periods of time without spoiling and could serve as a longlasting supply of food. The supplies of maize had to be stored somewhere, and the size of the great houses would make them very suitable for the purpose. A third theory proposes that houses were used as ceremonial centers. Close to one house, called Pueblo Alto, archaeologists identified an enormous mound formed by a pile of old material. Excavations of the mound revealed deposits containing a surprisingly large number of broken pots. This finding has been interpreted as evidence that people gathered at Pueblo Alto for special ceremonies. At the ceremonies, they ate festive meals and then discarded the pots in which the meals had been prepared or served. Such ceremonies have been documented for other Native American cultures. Listening Professor: Unfortunately none of the arguments about what the Chaco great houses were used for is convincing. First, sure, from the outside, the great houses look like later and Native American apartment but the inside of the great houses casts serious doubt on the idea that many people lived there. I39。t need the idea of endothermy and running to explain why dinosaurs evolved to have their legs under their bodies. Ok, so how about bone structure? Many dinosaur bones do have Haversian canals, that39。t prove the dinosaurs were endotherms.Well, what about the fact that dinosaurs have their legs placed under their bodies, not out to the side like crocodiles. That doesn39。s side, as they are for crocodiles and many lizards. The legs of all modern endotherms are underneath the body, and so were the legs of dinosaurs. This strongly suggests that dinosaurs were endotherms. Haversian canals There is also a connection between endothermy and bone structure. The bones of endotherms usually include structures called Haversian canals. These canals house nerves and blood vessels that allow the living animal to grow quickly, and rapid body growth is in fact a characteristic of endothermy. The presence of Haversian canals in bone is a strong indicator that the animal is an endotherm, and fossilized bones of dinosaurs are usually dense with Haversian canals. Listening Professor: Many scientists have problems with the arguments you read in the passage. They don39。C, no matter whether the environment is warm or cold. Because dinosaurs were reptiles, and modern reptiles are not endotherms, it was long assumed that dinosaurs were not endotherms. However, dinosaurs differ in many ways from modem reptiles, and there is now considerable evidence that dinosaurs were, in fact, endotherms. Polar dinosaurs One reason for believing that dinosaurs were endotherms is that dinosaur fossils have been discovered in Polar Regions. Only animals that can maintain a temperature well above that of the surrounding environment could be active in such cold climates. Leg position and movement There is a connection between endothermy and the position and movement of the legs. The physiology of endothermy allows sustained physical activity, such as running. But running is efficient only if an animal39。s face. That39。s indeed a work by Rembrandt. Here is why. First, the fur collar. Xrays and analysis of the pigments in the paint have shown that the fur collar wasn39。t move very quickly. Why? Because it took so long to reach consensus。t contribute much at all, but if their team did a good job, they nevertheless benefited from the recognition the team got. And what about group members who worked especially well and who provided a lot of insight on problems and issues? Well . . . the recognition for a job well done went to the group as a whole, no names were named. So it won39。t follow that once some employees choose a fourday workweek, many more jobs will bee available. Hiring new workers is costly, as I argued a moment ago. And panies have other options. They might just choose to ask their employees to work overtime to make up the difference. Worse, panies might raise expectations. They might start to expect that their fourday employees can do the same amount of work they used to do in five days. If this happens, then no additional jobs will