①熟石灰  ②石墨      ③干冰      ④甲烷      ⑤氢气      ⑥二氧化硫．

某公司一下属企业从事某种高科技产品的生产．该企业第一年年初有资金2000万元，将其投入生产，到当年年底资金增长了50%．预计以后每年年增长率与第一年的相同．公司要求企业从第一年开始，每年年底上缴资金d万元，并将剩余资金全部投入下一年生产．设第n年年底企业上缴资金后的剩余资金为a_n万元．

（Ⅰ）用d表示a₁，a₂，并写出a_n+1与a_n的关系式；

（Ⅱ）若公司希望经过m（m≥3）年使企业的剩余资金为4000万元，试确定企业每年上缴资金d的值（用m表示）．

    The day before Christmas I pulled into a store parking lot and counted my money again. It wasn't much. I 1 being poor, not having enough to 2 my small children a few simple toys. As I was 3 I noticed the Salvation Army (救世军) bell ringer at the4. I felt bad again because I didn't feel I could 5 anything to give him. I started walking towards the entrance 6 two cars entered empty parking spaces in front of me. The first was a7, new Cadillac which became the 8 of me the moment I saw it. “How 9 I thought, “would it be to have enough money to buy a car like that!” The second car10, was an ancient car more shabby than the one I was driving.

    A man got out of the Cadillac and hurried into the store 11 past the bell ringer without a second 12. Out of the old car came a young mother with three small children following 13 behind her. Her clothes looked as 14 as her car, yet she slopped at the entrance and 15 a bill. In that second a(n)16 touched me, my envy and dislike 17 me, and all the love and joy filled me. I fished a bill out of my own purse18 it in the Salvation Army kettle, and wished the 19 a “Merry Christmas!”

    Now I felt I was a poor man hut rich on the 20. After finding a few things for my kids, I drove home with my heart singing.