What new food product allowed rapid population growth in china during the song era

During the Song era, the new food product that allowed rapid population growth in China was rice which was distributed to prevent famine. The rice distributed prevented famine and led to a rapid increase in population during the Song era. Each year people grew a double crop which produced surplus rice which could be sold in the open market thus led to the accumulation of more wealth in rural areas.

Limit

Explanation:

If they limit their population growth then prices will not be so high. The less people, the lower the tax prices.