阅读理解

　　Do you know something about tree rings(年轮)? Do you know they can tell us what the weather was like, sometimes even hundreds of years ago?

　　A tree will grow well in a climate(气候)with lots of sunshine and rainfall．And little sunshine or rainfall will limit(限制)the growth of climate by studying the tree rings．For example, to find out the weather of ten years ago, count the rings of a tree from the outside to the inside．If the tenth ring is far from the eleventh ring, then we’re sure that it was sunny and rainy most of that year．If it is near to the eleventh ring, then the climate that year was bad．

　　Tree rings are important not only for studying the history 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 there－no trees and no people．What happened?

　　A scientist studied the rings of dead trees there．He found that the people had to leave because they had cut down all the trees to make fires and buildings．As all the trees had gone, the people there had to move．

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　　Do you hope to move to another city or a foreign country?It may be interesting．But how about moving to 　　1　　 planet?A US company now has a plan：sending people to Mars 　　2　　 20 years．

　　To begin with,the company plans to send 　　3　　 people to go to Mars first．It will 　　4　　 them several months to get there．When they arrive,they will build a 　　5　　 first．

　　But Mars is not an easy place to 　　6　　．It is rocky,cold and has lots of sandstorms(沙尘暴)．Also,there is 　　7　　 air for breath．So people would have to live in a special house．They would have to 　　8　　 special clothes if they go out．

　　People will have to find 　　9　　 resources(资源),iron,water and so on．All these could help people live there…

　　Sounds interesting?You might want to go to Mars now．　　10　　 will things go well as the company hopes?We'll wait and see．

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