Questions:
1. How long is the Great Wall?
2. When did it begin to be built?

 　The Great Wall is one of the wonders in the world architectural history. Starting from Shanhaiguan in the east and ending at Jiayuguan in the west, the Great Wall has a lengthabout 6,700 kilometers. The earliest part of the Wall was built during theWarring States Period(476-211 B.C.) and the project was continued in the following dynasties. 
　The section of the Wall at Badaling is a typical part of the Great Wall of the Ming Dynasty. It is in Yanqing County, about 75 km far from Beijing. The wall averages 7.8 meters in height, 6.5 meters wide at the base and 5.8 meters wide at the top. A watchtower was built every hundred meters.
　Besides the famous Badaling Section, Juyongguan Section, Jinshanling Section, Simatai Section, Shanhaiguan and Jiayuguan are attractive to the tourists from the world.