The Great Wall of China is one of the most important _______wonders and the largest building project in the world. In the past, the Great Wall served to _______ the border. Now it is regarded as a(n) _______oft he Chinese nation. The Great Wall _______across China's landscape like a huge dragon, rising and falling with the contours of the_______.When people walk on it they are walking on history, which is totally _______.
选项：

A:

snakes

B:

man-made

C:

unique

D:

symbol

E:

mountain

F:

defend