题目

Harvard researchers have created a tough, low-cost, biodegradable (可生物降解的) material inspired by insects hard outer shells. The materials inventors say it has a number of possible uses and someday could provide a more environmentally friendly alternative to plastic. The material, made from shrimp (虾) shells and proteins produced from silk, is called shrilk. It is thin, clear, flexible and strong.    A major benefit of the material is its biodegradability. Plastics toughness and flexibility represented a revolution in materials science during the 1950s and 60s. Decades 下图中阴影部分表示林地、空白部分表示沙地。若此时反映的是北半 球中纬度某地区的夏季白天的情况。回答以下23-24题。 23.图中甲、丙两处的风向分别是                    A．西风和东风        B．西北风和东南风 C．东南风和西北风    D．西南风和东北风 24.目前，有部分城市在城郊建设人工生态林，此举的意义在于   ①减少风沙对城市的侵袭    ②减少郊区工厂的污染物带入城市   ③避免城市的污染场带到郊区  ④避免城市出现“热岛效应” A．③④    B．①②    C．①②③  D．①③④