根据短文内容，从下面的选项中选出可以填入空白处的最佳选项。有一项为多余选项。
China is the country with a long history and many amazing ancient buildings. The Great Wall and the Forbidden City are the most famous. 1. Every year, they attract millions of tourists from all over the world to enjoy their beauty and try to find out the secrets behind them.
The first one is the Great Wall. It is one of the longest walls in the world. In ancient times, people built the wall to protect their country and keep enemies away. However, many mysteries still remain. How did ancient people carry huge and heavy stones to the top of high mountains without modern machines? 2. They worked in very hard conditions with simple tools. Many workers spent their whole lives on this project. Some even lost their lives in the process. Until now, some parts of the wall are still being studied, and new facts are still being discovered.
The second one is the Forbidden City in Beijing. 3. For about 500 years, 24 emperors lived and worked there. It is one of the largest and best-kept palaces in the world. The Forbidden City also has many interesting mysteries. 4. People wonder how ancient designers made the buildings not only beautiful but also very strong. Even after hundreds of years, most buildings still look great.
Today, both the Great Wall and the Forbidden City are world-famous cultural relics. 5. They take photos, listen to stories, and feel the long history of China. As time goes by, more secrets may be discovered, and these ancient places will keep attracting and surprising people for many more years.

1.B 2.D 3.A 4.E 5.C

我们可以根据上下文逻辑逐一匹配选项：
1. 空前提到长城和紫禁城是中国最著名的古建，空后提到它们吸引游客探寻背后的秘密，B选项“它们不仅是伟大的奇迹，还承载着许多有趣的谜团”可以承上启下，符合语境。
2. 空前提到疑问：没有现代机械古人如何将巨石运到山顶，空后描述工人们用简陋工具艰苦劳作，D选项“成千上万的普通人参与了它的建造”衔接前后内容，逻辑通顺。
3. 空后提到有24位皇帝在此居住工作了约500年，A选项“它曾是中国皇帝的居所”和后文内容直接对应。
4. 空后提到人们好奇古代设计师如何让建筑既美观又坚固，E选项“它宏伟的设计背后有很多有趣的故事”引出关于建筑设计的相关谜团，符合语境。
5. 空后描述游客拍照、听故事、感受中国历史的行为，C选项“每年有数百万游客前来参观它们”引出后文的游客行为，逻辑匹配。
多余选项F和全文内容没有对应衔接的位置。