等比数列{a_n}的前n项和为S_n，已知S₁，2S₂，3S₃成等差数列，则{a_n}的公比为____ 

阅读理解。

    Amy and Sarah are good friends. They are from America. They like winter in America because there are many activities in winter. They can make a snowman,go fishing and go skiing with many friends. There are two festivals (节目) in winter. They're Christmas Day and Thanksgiving. Amy and Sarah are very happy. But they're in Beijing now. They like winter in Beijing, too. Because It's beautiful. It's windy and cold. They're going to visit the Great Wall, so they're very happy.

“三月的横断山区，山顶白雪皑皑，山脚百花争艳”，说明气温分布受（    ）影响。