【单选题】

Do you know something about tree ringsDo you know they can tell us what the weather was like, sometimes even hundreds of years ago

We can see the change of weather by studying the tree rings.
For example, to find out the weather of ten years ago, count (数) the rings of a tree from outside to the inside. If the tenth ring is far from the eleventh ring, then we are sure that it was sunny most of that year. If it is near to the eleventh ring, then the weather that year was baD、
Tree rings are important not only for studying the history (历史) of weather but also for studying the history of man. Many centuries ago there lived a lot of people at a place in New Mexico.But now you can find only sand thereA、scientist studied the rings of dead trees there. He found that the people had to leave because they had cut down all trees to make fires and buildings.As all trees had gone, the people there had to move.
What happened to those people who had once lived in New MexicoA．They are still living there.
B．They had all died because the trees there had dieD、
C．They moved to other places because all the trees were cut down.