The strong agriculture and trading affected china because under the song, the amount of land increased and they traded with china
A personal opinion that is not based on evidence
Probably so they could be sold for more money and so they'd look healthy and strong
The correct answer is gypsum.
Indeed, as the name indicates it, gypsum is used in the production of plaster, fertilizer, soil conditioner, cement, food additives, etc.
Gypsum has been used for millennia in China as an ingredient of traditional Chinese medicine and in the Middle Ages as a component of gesso (a white paint used for artworks of several kinds).
