题目

   have   building   each   look  first   they  in  enough  finish  but  much  at Do you know the differences between the new building and the old ones? Old buildings     1     brick(砖)and stone walls. The walls hold up the  2 . In cities, many modern building     3    as if they are made just of windows. Walls of dark glass reach high into the air. Many buildings are    4   than 50 stories(层)tall. Are walls of glass strong    5    to hold up the new buildings? No, The new glass walls do not hold up the buildings,    6    they o通常在十字路口安装的监控摄像头可以拍下违章行驶的汽车照片，观察照片我们可以发现，车的外部很清楚，但几乎看不见车内的人．这是为什么？