原文：
长城是世界一大奇迹。现在，每年都有几百万人到长城游览。在旺季，几处最著名的景点总是让成群结队的游客挤得水泄不通。中国人修筑长城的历史久远，可以追溯到战国时期(Warring State period)。历史上，中国共修过大约20座长城。在所有这些长城中，明长城最长，达到6700公里。在当时，中国技术在世界上处于领先地位，因此明长城的结构也是最复杂的。明长城的修筑是为了抵御北方游牧民族的入侵。
翻译：
The Great Wall is a wonder of the world. Now, millions of people journey to the Great Wall each year, making its most popular sites besieged by hordes of tourists during busy season. The Chinese have a long history of building walls, dating from the Warring State period. In history, about 20 walls were built, with the wall constructed during the Ming Dynasty being the longest, extending 6700km. China was the most technology advanced nation in the world then, so the wall was also the most sophisticated in structure. It was built to ward off the invasion of nomads from the north.
重点词汇：
世界七大奇迹 the seven wonders of the world
旺季 busy seasons 淡季 slack seasons
成群结队 hordes of tourists
追溯 dating from
