1. 5,500 miles

2. To keep out the Mongols. from Hushan to Jiayuguan Pass

3. The extreme mountains in the east

4. 500,000 square miles

5. North china plain adn the Manchuria plain

6. the yellow, the Yangtze, and the Xi Jiang

7. From the Kunlun mountains to Lanzhou

8. 5,000 miles

9. the Xi Jiang

10. rice, soy, iron, oil

11. Japan, and Taiwan

12. China became self-sufficient, while Japan and other countries require trade to grow

13. a water twister, and in the waters of the south pacific

14. cold and dry

15. northeast

16. In hainan and Taiwan

17. a water twister