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。

参考答案:

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.

1.“长城是世界一大奇迹”翻译为“the Great Wall is a wonder of the world”。奇迹在英语中一般用wonder。在最著名的the seven wonders of the world(世界七大奇迹)中，长城也是其中之一。

2.旺季 busy seasons旺季就是热销的季节，生意也就特别忙活，所以这里用“忙活的季节”来翻译，可以体现出译者的变通能力。淡季可相应翻译为slack seasons。

3.成群结队 hordes of touristsHorde大群人，还可译成“a huge crowd/throng”。

4.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。Now, millions of people journey to the Great Wall each year, making its most popular sites besieged by hordes of tourists during busy season.这里要用合句翻译法，把原文中的第二句译成第一句的伴随状语。即把原文中两个有一定关系的简单句合为一个句子，且句意不变。

5. 追溯 dating from常用来表示“追溯”的短语还有：date back to。