【简答题】The world of the science-fiction 3-D film Avatar is so perfect that the line between fact and fiction has become somewhat blurred (模糊) . Movie-goers have admitted being annoyed by depression at not be...
【单选题】如图 3, 小玲设计用手电来测量某古城墙高度.在点 P 处放一水平的平面镜,光线从点 A 出发经平面镜反射后,刚好射到古城墙 CD 的顶端 C 处.已知 AB ⊥ BD , CD ⊥ BD ,且测得 AB = 1.4 m , BP = 2.1 m , PD = 12 m .那么该古城墙 CD 的高度是 ( ) m.