题目

Who g building the new China? It′s not the factory owners or the business men and women of China．It′s someone else．It′s the people who have left their homes to follow their dreams，the dream of a better life．    We see them every day，on every street corner，on every construction site in cities．They work day and night in the terrible working conditions and weather．They build the roads the theaters，the cinemas，and the supermarkets．They even clean up our rubbish．They are China′s migrant workers (民工)．Young and old，these men and women are building the new Chi设数列的前n项和为，且满足，n=1,2,3,…. （Ⅰ）求数列的通项公式； （Ⅱ）若数列满足，且，求数列的通项公式．