题目

阅读理解Whenyou buy fresh-cut flowers, do you think about where they came from？You might think they were grown somewhere nearby. The reality,though, is that the cut flower trade is increasingly International. Today,thanks to airplanes and high-tech cooling systems, even the most delicateflower be exported and sold thousands of kilometers away from where it wasgrown.The Netherlands handles about 60 percent of the world's cut flowers. And its auction houses (拍卖行) are very large—Aalsmeer, near Amsterdam, is auction house in the sense that Tokyo is a city, or Everest a mountain. Abou小刚家装修，准备安装照明灯．他和爸爸到市场进行调查，了解到某种优质品牌的一盏40瓦白炽灯的售价为1.5元，一盏8瓦节能灯的售价为22.38元，这两种功率的灯发光效果相当．假定电价为0.45元／度，设照明时间为x(小时)，使用一盏白炽灯和一盏节能灯的费用分别为y1(元)和y2(元)[耗电量(度)＝功率(千瓦)×用电时间(小时)，费用＝电费＋灯的售价]．(1)分别求出y1，y2与照明时间x之间的函数表达式；(2)你认为选择哪种照明灯合算？(3)若一盏白炽灯的使用寿命为2000小时，一盏节能灯的使用寿命为6000小时，如果不考虑其他因素，以6000小时计算，使用哪种照明灯省钱？省多少钱？