题目原文：

As early as the twelfth century A.D., 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 competing 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, well-known "apartment buildings" at Taos, New Mexico, in which many people have been living for centuries.

A second theory contends that the Chaco structures were usedto 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 long-lasting 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.

 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.
 I'll explain.
 If hundreds of people were living in the great houses, then there would have to be many fireplaces, where each family did its daily cooking, but there are very few fireplaces.
 In one of the largest great houses, there were fireplaces for only around ten families.
 Yet there were enough rooms in the great house for more than a hundred families, so the primary function of the houses couldn't have been residential.
 Second, the idea that the great houses were used to store grain maize ; unsupported by evidence.
 It may sound plausible that large empty rooms were used for storage, but excavations of the great houses have not uncovered many traces of maize or maize containers.
 If the great houses were used for storage, why isn't there more spilled maize on the floor?
 Why aren't there more remains of big containers?
 Third, the idea that the great houses were ceremonial centers isn't well supported either.
 You know that mound at Pueblo Alto?
 It contains lots of other materials besides broken pots, stuff you wouldn't expect from ceremonies.
 For example, there are large quantities of building materials, sands, stones, even construction tools.
 This suggests that the mound is just a trash heap of construction material, stuff that was thrown away or not used up when a house was being built.
 The pots in the pile could be regular trash too, leftover from the meals of the construction workers.
 So the Pueblo Alto mound is not good evidence that the great houses were used for special ceremonies.