如图是一位同学设计的用手电筒来测量某古城墙高度的示意图．点P处放一水平的平面镜，光线从点A出发经平面镜反射后刚好到古城墙CD的顶端C处，已知AB⊥BD，CD⊥BD，测得AB=2米，BP=3米，PD=12米，那么该古城墙的高度CD是 ____米．

如图，在平面直角坐标系中，直线y=﹣2x+10与x轴，y轴相交于A，B两点，点C的坐标是（8，4），连接AC，BC．

猜数字游戏中，小明写出如下一组数： $\frac{2}{5}$ ， $\frac{4}{7}$ ， $\frac{8}{11}$ ， $\frac{16}{19}$ ， $\frac{32}{35}$ …，小亮猜想出第六个数字是 $\frac{64}{67}$ ，根据此规律，第n个数是____．

如图所示是一登山运动员从拉萨攀登到珠峰峰顶的线路示意图，由此可判断下列说法正确的是（　　）

         Life in the 21st century will be different from lire in the 20th century because many changes will take place in the new century．But what will the changes be?   

    The population is  1  fast．There will be more and more people in the world and most of them will live 2than before，because life will be better．3 will be much smaller and more useful，and there will be at least one in every home．And computer studies will be one of the important 4  for students at school．People will have more free time for sports and  5 TV．Travelling will also become  6   because of modern transportation(交通)．There will be changes in our food，too．More land will be used for building new towns and houses．Then there will be less room for cows and sheep，so  7  will be more expensive．Maybe no one will eat it every day．  8 ，they eat more vegetables and fruits．Maybe people will be healthier．Work in the future will be  9  ，too．Dangerous and hard work will be done by robots．Because of this，many people will 10  their jobs. This will also be a problem．