大家好！上周我们一起认识了第4、5、6名动物建筑师。它们分别是珊瑚虫、鸟和鼹鼠。Who are the top three? Let's visit them now. Do you know this guy? He loves swimming. He also loves building dams. People built the first dam in Egypt (埃及) 5,000 years ago. 而海狸从500万年前就开始建造大坝了...