题目

Urbanization Until relatively recently, the vast majority of human beings lived and died without ever seeing a city. The first city was probably founded no more than 5,500 years ago.     38._ . In fact, nearly everyone lived on farms or in tiny rural (乡村的) villages. It was not until the 20th century that Great Britain became the first urban society in history— a society in which the majority of people live in cities and do not farm for a living. Britain was only the beginning. 39._   .The process of urbanization— the migration (迁移) of people from the countryside to t如图，路边有一根电线杆AB和一块半圆形广告牌，在太阳光照射下，杆顶A的影子刚好落在半圆形广告牌的最高处G，而半圆形广告牌的影子刚好落在平地上一点E，若BC=5米，半圆形的广告牌直径为6米，DE=2米．（1）求电线杆落在广告牌上的影子长（即︵CG的长）．（2）求电线杆的高度．