The Great Wall of China is the longest wall in the world. It is more than 6000 kilometres long, about 7 metres high, 5 to 6 metres wide. It is known to be the only one of the structures(建筑物) built by men on Earth that can be seen from the moon.The Potala(布达拉宫) in Tibet, China, is the world's highest palace. It is over 3 kilometres above the sea level.The Great Pyramid(金字塔) in Egypt is the biggest burial(埋葬) place ever built. It is about 137 metres high, or about the height of 40-storey building. Each side of the Pyramid is about 230 metres long, or about as long as 2 city blocks.The Sears Tower in Chicago, U.S.A., reaches a height of 443 metres. It has 110 storeys and covers a total floor space of 420,000 square metres. It is the tallest office building in the world.1)、The Great Wall of China is the longest wall in the world because it is over six thousand kilometers long.