Why was prosperity during the Song dynasty higher than it was before or after?

What parts of the economy account for the greater income achieved during this period? b. How was government economic policy different during the Song dynasty compared to the dynasties before and after? c. What social or technological changes occurred that made the higher prosperity possible? d. What was the foreign policy of China like during the Song dynasty, and how did that affect the Chinese economy? e. Did the increase in prosperity during this period affect average people (e.g., farmers) or only benefit the elites of Chinese society?