1. C. The Great Wall of China is called the "Ten Thousand- Li Great Wall" in Chinese. Actually, it is over 6,000 kilometers in length. It has a history of more than twenty centuries

2. B. Parts of it were built through different dynasties. In order to protect his empire from the enemy in the north, Emperor Qin Shi Huang had all the walls joined up. Thus the Great Wall began to exist

3. E. The Great Wall is wide enough at the top for five horses and ten men to walk side by side. Along the wall are watchtowers, where soldiers used to be stationed to guard the country

4. D. When the enemy came, fires were lit and guns were fired to warn soldiers at other towers. In this way, a warning message could be sent quickly 

5. A. the Great Wall has become the symbol of China. And it is one of the few objects built by man that can be seen on the moon

PART 7

1. H. flying

2. B. before

3. K. designing

4. A. trained

5. I. mission

6. M. landed

7. D. because

8. J. step

9. E. mankind

10. C. experiments