题目

Welcome to Germany’s largest theme park! In an area covering 68 hectares, visitors to Europa Park can experience the architecture, plants and culture of 12 European countries.      Set in various themed areas, the popular leisure(休闲)park provides over 100 attractions and wonderful shows. Visitors can take a leisure walk through Italy, France, Spain, Portugal and Scandinavia in one afternoon!      Visitors can experience the rush of our high speed roller coasters, watch various acrobatic (杂技的) shows in our international programs, get lost in the underwater world fro(2007，内蒙古包头市，16)经过两年的连续治理，某城市的大气环境有了明显改善，其每月每平方公里的降尘量从50吨下降到40.5吨，则平均每年下降的百分率是________．