It was invented by the ancient egyptians who began growing plant in containers
Well the class structure was lords then samurais then farmers. How it stabilized society was it set a strict code to follow for each of the classes and they followed that. How it unified? I'm not so sure but my guess is that every person in each class fought for their power like the lords or for their land like the farmers.
The correct answer is "D. Reinvent". The 5Rs is a method of how to reduce your environmental impact in your workplace or at home. Following this thought, you need to Rethink your way to do things; Refuse actions or goods not sustainable (like plastic bags); Reduce your amount of daily waste; Reuse items instead of throwing it out when it is possible; and Recycle as much as you can. All these actions together help the planet.
When there is more of a product, the price is lowered because the product is not in short supply. However, if there is very little of the product, the price will increase because it is harder to get one's hands on that product because of its scarcity.